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 $62.76   3.596%   $65.0168   $65.02   $65.00   $65.00  
  Purchase #2 $184.46   4.854%   $193.4137   $193.41   $193.40   $193.40  
  Purchase #3 $246.54   12.132%   $276.4502   $276.45   $276.45   $276.50  
  Purchase #4 $191.32   13.350%   $216.8612   $216.86   $216.85   $216.90  
  Purchase #5 $142.46   4.520%   $148.8992   $148.90   $148.90   $148.90  
  Purchase #6 $222.81   5.118%   $234.2134   $234.21   $234.20   $234.20  
  Purchase #7 $128.72   12.626%   $144.9722   $144.97   $144.95   $145.00  
  7 purchase totals = $1,179.07       $1,279.8267   $1,279.82   $1,279.75   $1,279.90