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 $95.57   6.106%   $101.4055   $101.41   $101.40   $101.40  
  Purchase #2 $188.85   3.144%   $194.7874   $194.79   $194.80   $194.80  
  Purchase #3 $45.84   7.274%   $49.1744   $49.17   $49.15   $49.20  
  Purchase #4 $62.44   12.550%   $70.2762   $70.28   $70.30   $70.30  
  Purchase #5 $83.31   10.824%   $92.3275   $92.33   $92.35   $92.30  
  Purchase #6 $109.31   11.788%   $122.1955   $122.20   $122.20   $122.20  
  Purchase #7 $90.75   12.399%   $102.0021   $102.00   $102.00   $102.00  
  7 purchase totals = $676.07       $732.1686   $732.18   $732.20   $732.20