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 $31.59   10.759%   $34.9888   $34.99   $35.00   $35.00  
  Purchase #2 $87.90   7.448%   $94.4468   $94.45   $94.45   $94.40  
  Purchase #3 $179.29   12.637%   $201.9469   $201.95   $201.95   $201.90  
  Purchase #4 $228.62   6.439%   $243.3408   $243.34   $243.35   $243.30  
  Purchase #5 $91.67   12.210%   $102.8629   $102.86   $102.85   $102.90  
  Purchase #6 $185.50   7.663%   $199.7149   $199.71   $199.70   $199.70  
  Purchase #7 $96.54   3.710%   $100.1216   $100.12   $100.10   $100.10  
  7 purchase totals = $901.11       $977.4227   $977.42   $977.40   $977.30