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 $39.66   11.437%   $44.1959   $44.20   $44.20   $44.20  
  Purchase #2 $175.27   6.330%   $186.3646   $186.36   $186.35   $186.40  
  Purchase #3 $184.70   9.833%   $202.8616   $202.86   $202.85   $202.90  
  Purchase #4 $248.66   11.507%   $277.2733   $277.27   $277.25   $277.30  
  Purchase #5 $46.30   6.202%   $49.1715   $49.17   $49.15   $49.20  
  Purchase #6 $145.44   8.657%   $158.0307   $158.03   $158.05   $158.00  
  Purchase #7 $57.55   8.179%   $62.257   $62.26   $62.25   $62.30  
  7 purchase totals = $897.58       $980.1546   $980.15   $980.10   $980.30