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 $66.56   7.266%   $71.3962   $71.40   $71.40   $71.40  
  Purchase #2 $97.61   7.328%   $104.7629   $104.76   $104.75   $104.80  
  Purchase #3 $212.25   3.577%   $219.8422   $219.84   $219.85   $219.80  
  Purchase #4 $184.31   9.491%   $201.8029   $201.80   $201.80   $201.80  
  Purchase #5 $8.41   13.780%   $9.5689   $9.57   $9.55   $9.60  
  Purchase #6 $139.52   7.227%   $149.6031   $149.60   $149.60   $149.60  
  Purchase #7 $234.74   5.111%   $246.7376   $246.74   $246.75   $246.70  
  7 purchase totals = $943.40       $1,003.7138   $1,003.71   $1,003.70   $1,003.70