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 $102.95   4.667%   $107.7547   $107.75   $107.75   $107.80  
  Purchase #2 $190.72   5.283%   $200.7957   $200.80   $200.80   $200.80  
  Purchase #3 $51.65   3.664%   $53.5425   $53.54   $53.55   $53.50  
  Purchase #4 $222.43   6.415%   $236.6989   $236.70   $236.70   $236.70  
  Purchase #5 $111.30   7.270%   $119.3915   $119.39   $119.40   $119.40  
  Purchase #6 $68.81   12.450%   $77.3768   $77.38   $77.40   $77.40  
  Purchase #7 $177.95   5.163%   $187.1376   $187.14   $187.15   $187.10  
  7 purchase totals = $925.81       $982.6977   $982.70   $982.75   $982.70