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 $106.71   11.213%   $118.6754   $118.68   $118.70   $118.70  
  Purchase #2 $146.71   4.424%   $153.2005   $153.20   $153.20   $153.20  
  Purchase #3 $99.41   11.556%   $110.8978   $110.90   $110.90   $110.90  
  Purchase #4 $24.54   5.593%   $25.9125   $25.91   $25.90   $25.90  
  Purchase #5 $204.65   11.456%   $228.0947   $228.09   $228.10   $228.10  
  Purchase #6 $34.56   3.502%   $35.7703   $35.77   $35.75   $35.80  
  Purchase #7 $27.42   4.549%   $28.6673   $28.67   $28.65   $28.70  
  7 purchase totals = $644.00       $701.2185   $701.22   $701.20   $701.30