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 $134.84   13.799%   $153.4466   $153.45   $153.45   $153.40  
  Purchase #2 $215.54   3.247%   $222.5386   $222.54   $222.55   $222.50  
  Purchase #3 $186.76   11.197%   $207.6715   $207.67   $207.65   $207.70  
  Purchase #4 $53.43   7.234%   $57.2951   $57.30   $57.30   $57.30  
  Purchase #5 $21.96   10.164%   $24.192   $24.19   $24.20   $24.20  
  Purchase #6 $191.28   11.622%   $213.5106   $213.51   $213.50   $213.50  
  Purchase #7 $66.51   13.761%   $75.6624   $75.66   $75.65   $75.70  
  7 purchase totals = $870.32       $954.3168   $954.32   $954.30   $954.30