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 $59.57   9.783%   $65.3977   $65.40   $65.40   $65.40  
  Purchase #2 $53.25   11.452%   $59.3482   $59.35   $59.35   $59.30  
  Purchase #3 $16.90   9.574%   $18.518   $18.52   $18.50   $18.50  
  Purchase #4 $200.34   4.681%   $209.7179   $209.72   $209.70   $209.70  
  Purchase #5 $232.62   4.742%   $243.6508   $243.65   $243.65   $243.70  
  Purchase #6 $144.70   8.569%   $157.0993   $157.10   $157.10   $157.10  
  Purchase #7 $92.38   10.780%   $102.3386   $102.34   $102.35   $102.30  
  7 purchase totals = $799.76       $856.0705   $856.08   $856.05   $856.00