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 $210.32   11.836%   $235.2135   $235.21   $235.20   $235.20  
  Purchase #2 $94.79   8.432%   $102.7827   $102.78   $102.80   $102.80  
  Purchase #3 $123.62   8.628%   $134.2859   $134.29   $134.30   $134.30  
  Purchase #4 $192.67   9.605%   $211.176   $211.18   $211.20   $211.20  
  Purchase #5 $154.79   8.872%   $168.523   $168.52   $168.50   $168.50  
  Purchase #6 $60.71   6.202%   $64.4752   $64.48   $64.50   $64.50  
  Purchase #7 $236.45   12.418%   $265.8124   $265.81   $265.80   $265.80  
  7 purchase totals = $1,073.35       $1,182.2687   $1,182.27   $1,182.30   $1,182.30