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 $238.35   4.261%   $248.5061   $248.51   $248.50   $248.50  
  Purchase #2 $176.53   5.504%   $186.2462   $186.25   $186.25   $186.20  
  Purchase #3 $14.88   6.474%   $15.8433   $15.84   $15.85   $15.80  
  Purchase #4 $64.55   4.192%   $67.2559   $67.26   $67.25   $67.30  
  Purchase #5 $240.96   10.645%   $266.6102   $266.61   $266.60   $266.60  
  Purchase #6 $189.82   12.293%   $213.1546   $213.15   $213.15   $213.20  
  Purchase #7 $189.66   6.868%   $202.6858   $202.69   $202.70   $202.70  
  7 purchase totals = $1,114.75       $1,200.3021   $1,200.31   $1,200.30   $1,200.30