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 $59.38   8.766%   $64.5853   $64.59   $64.60   $64.60  
  Purchase #2 $116.67   4.583%   $122.017   $122.02   $122.00   $122.00  
  Purchase #3 $205.72   8.285%   $222.7639   $222.76   $222.75   $222.80  
  Purchase #4 $95.36   7.461%   $102.4748   $102.47   $102.45   $102.50  
  Purchase #5 $131.40   7.818%   $141.6729   $141.67   $141.65   $141.70  
  Purchase #6 $81.41   8.319%   $88.1825   $88.18   $88.20   $88.20  
  Purchase #7 $238.78   11.202%   $265.5281   $265.53   $265.55   $265.50  
  7 purchase totals = $928.72       $1,007.2245   $1,007.22   $1,007.20   $1,007.30