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 $67.51   8.399%   $73.1802   $73.18   $73.20   $73.20  
  Purchase #2 $233.30   7.845%   $251.6024   $251.60   $251.60   $251.60  
  Purchase #3 $54.51   12.316%   $61.2235   $61.22   $61.20   $61.20  
  Purchase #4 $56.66   6.397%   $60.2845   $60.28   $60.30   $60.30  
  Purchase #5 $25.49   7.550%   $27.4145   $27.41   $27.40   $27.40  
  Purchase #6 $214.88   10.807%   $238.1021   $238.10   $238.10   $238.10  
  Purchase #7 $91.96   12.861%   $103.787   $103.79   $103.80   $103.80  
  7 purchase totals = $744.31       $815.5942   $815.58   $815.60   $815.60