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 $59.28   12.687%   $66.8009   $66.80   $66.80   $66.80  
  Purchase #2 $244.94   13.758%   $278.6388   $278.64   $278.65   $278.60  
  Purchase #3 $59.70   8.814%   $64.962   $64.96   $64.95   $65.00  
  Purchase #4 $98.44   3.626%   $102.0094   $102.01   $102.00   $102.00  
  Purchase #5 $179.98   5.350%   $189.6089   $189.61   $189.60   $189.60  
  Purchase #6 $154.41   13.736%   $175.6198   $175.62   $175.60   $175.60  
  Purchase #7 $6.32   8.114%   $6.8328   $6.83   $6.85   $6.80  
  7 purchase totals = $803.07       $884.4726   $884.47   $884.45   $884.40