Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $162.31   13.489%   $184.204   $184.20   $184.20   $184.20  
  Purchase #2 $125.75   12.808%   $141.8561   $141.86   $141.85   $141.90  
  Purchase #3 $236.94   13.169%   $268.1426   $268.14   $268.15   $268.10  
  Purchase #4 $153.47   5.862%   $162.4664   $162.47   $162.45   $162.50  
  Purchase #5 $120.65   12.178%   $135.3428   $135.34   $135.35   $135.30  
  Purchase #6 $218.29   8.148%   $236.0763   $236.08   $236.10   $236.10  
  Purchase #7 $157.61   5.696%   $166.5875   $166.59   $166.60   $166.60  
  7 purchase totals = $1,175.02       $1,294.6757   $1,294.68   $1,294.70   $1,294.70