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 $190.51   10.739%   $210.9689   $210.97   $210.95   $211.00  
  Purchase #2 $136.63   13.386%   $154.9193   $154.92   $154.90   $154.90  
  Purchase #3 $166.26   7.222%   $178.2673   $178.27   $178.25   $178.30  
  Purchase #4 $145.31   5.399%   $153.1553   $153.16   $153.15   $153.20  
  Purchase #5 $135.92   9.320%   $148.5877   $148.59   $148.60   $148.60  
  Purchase #6 $141.67   6.410%   $150.751   $150.75   $150.75   $150.80  
  Purchase #7 $33.66   6.370%   $35.8041   $35.80   $35.80   $35.80  
  7 purchase totals = $949.96       $1,032.4536   $1,032.46   $1,032.40   $1,032.60