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 $46.39   5.103%   $48.7573   $48.76   $48.75   $48.80  
  Purchase #2 $113.89   11.367%   $126.8359   $126.84   $126.85   $126.80  
  Purchase #3 $17.59   5.546%   $18.5655   $18.57   $18.55   $18.60  
  Purchase #4 $41.47   10.534%   $45.8384   $45.84   $45.85   $45.80  
  Purchase #5 $236.26   6.454%   $251.5082   $251.51   $251.50   $251.50  
  Purchase #6 $132.41   5.702%   $139.96   $139.96   $139.95   $140.00  
  Purchase #7 $43.37   4.227%   $45.2032   $45.20   $45.20   $45.20  
  7 purchase totals = $631.38       $676.6685   $676.68   $676.65   $676.70