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 $62.59   10.180%   $68.9617   $68.96   $68.95   $69.00  
  Purchase #2 $162.82   11.613%   $181.7283   $181.73   $181.75   $181.70  
  Purchase #3 $150.30   6.462%   $160.0124   $160.01   $160.00   $160.00  
  Purchase #4 $146.39   4.335%   $152.736   $152.74   $152.75   $152.70  
  Purchase #5 $165.68   3.162%   $170.9188   $170.92   $170.90   $170.90  
  Purchase #6 $34.66   13.673%   $39.3991   $39.40   $39.40   $39.40  
  Purchase #7 $144.77   7.304%   $155.344   $155.34   $155.35   $155.30  
  7 purchase totals = $867.21       $929.1003   $929.10   $929.10   $929.00