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 $46.63   13.840%   $53.0836   $53.08   $53.10   $53.10  
  Purchase #2 $127.95   5.799%   $135.3698   $135.37   $135.35   $135.40  
  Purchase #3 $148.71   11.613%   $165.9797   $165.98   $166.00   $166.00  
  Purchase #4 $199.64   3.563%   $206.7532   $206.75   $206.75   $206.80  
  Purchase #5 $95.46   7.287%   $102.4162   $102.42   $102.40   $102.40  
  Purchase #6 $241.98   9.303%   $264.4914   $264.49   $264.50   $264.50  
  Purchase #7 $159.99   5.125%   $168.1895   $168.19   $168.20   $168.20  
  7 purchase totals = $1,020.36       $1,096.2834   $1,096.28   $1,096.30   $1,096.40