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 $46.64   13.842%   $53.0959   $53.10   $53.10   $53.10  
  Purchase #2 $240.91   13.555%   $273.5654   $273.57   $273.55   $273.60  
  Purchase #3 $105.93   12.230%   $118.8852   $118.89   $118.90   $118.90  
  Purchase #4 $28.58   8.157%   $30.9113   $30.91   $30.90   $30.90  
  Purchase #5 $109.94   3.105%   $113.3536   $113.35   $113.35   $113.40  
  Purchase #6 $239.42   12.779%   $270.0155   $270.02   $270.00   $270.00  
  Purchase #7 $80.65   8.580%   $87.5698   $87.57   $87.55   $87.60  
  7 purchase totals = $852.07       $947.3967   $947.41   $947.35   $947.50