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 $66.27   3.535%   $68.6126   $68.61   $68.60   $68.60  
  Purchase #2 $216.87   5.871%   $229.6024   $229.60   $229.60   $229.60  
  Purchase #3 $61.53   9.242%   $67.2166   $67.22   $67.20   $67.20  
  Purchase #4 $153.60   7.404%   $164.9725   $164.97   $164.95   $165.00  
  Purchase #5 $57.51   3.497%   $59.5211   $59.52   $59.50   $59.50  
  Purchase #6 $92.44   12.721%   $104.1993   $104.20   $104.20   $104.20  
  Purchase #7 $243.64   11.715%   $272.1824   $272.18   $272.20   $272.20  
  7 purchase totals = $891.86       $966.3069   $966.30   $966.25   $966.30