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 $136.64   12.598%   $153.8539   $153.85   $153.85   $153.90  
  Purchase #2 $232.95   13.184%   $263.6621   $263.66   $263.65   $263.70  
  Purchase #3 $202.54   10.465%   $223.7358   $223.74   $223.75   $223.70  
  Purchase #4 $185.61   11.432%   $206.8289   $206.83   $206.85   $206.80  
  Purchase #5 $71.84   12.261%   $80.6483   $80.65   $80.65   $80.60  
  Purchase #6 $205.37   4.793%   $215.2134   $215.21   $215.20   $215.20  
  Purchase #7 $16.67   11.109%   $18.5219   $18.52   $18.50   $18.50  
  7 purchase totals = $1,051.62       $1,162.4643   $1,162.46   $1,162.45   $1,162.40