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 $53.75   7.312%   $57.6802   $57.68   $57.70   $57.70  
  Purchase #2 $168.58   3.588%   $174.6287   $174.63   $174.65   $174.60  
  Purchase #3 $97.27   11.149%   $108.1146   $108.11   $108.10   $108.10  
  Purchase #4 $71.41   8.591%   $77.5448   $77.54   $77.55   $77.50  
  Purchase #5 $158.37   7.663%   $170.5059   $170.51   $170.50   $170.50  
  Purchase #6 $175.36   7.595%   $188.6786   $188.68   $188.70   $188.70  
  Purchase #7 $134.66   7.588%   $144.878   $144.88   $144.90   $144.90  
  7 purchase totals = $859.40       $922.0308   $922.03   $922.10   $922.00