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 $232.83   10.596%   $257.5007   $257.50   $257.50   $257.50  
  Purchase #2 $54.68   11.115%   $60.7577   $60.76   $60.75   $60.80  
  Purchase #3 $157.48   13.168%   $178.217   $178.22   $178.20   $178.20  
  Purchase #4 $148.56   3.592%   $153.8963   $153.90   $153.90   $153.90  
  Purchase #5 $21.85   12.865%   $24.661   $24.66   $24.65   $24.70  
  Purchase #6 $71.82   8.435%   $77.878   $77.88   $77.90   $77.90  
  Purchase #7 $116.75   7.715%   $125.7573   $125.76   $125.75   $125.80  
  7 purchase totals = $803.97       $878.6680   $878.68   $878.65   $878.80