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 $211.41   13.803%   $240.5909   $240.59   $240.60   $240.60  
  Purchase #2 $178.67   4.348%   $186.4386   $186.44   $186.45   $186.40  
  Purchase #3 $107.66   4.763%   $112.7878   $112.79   $112.80   $112.80  
  Purchase #4 $107.45   3.550%   $111.2645   $111.26   $111.25   $111.30  
  Purchase #5 $197.51   6.345%   $210.042   $210.04   $210.05   $210.00  
  Purchase #6 $39.29   13.397%   $44.5537   $44.55   $44.55   $44.60  
  Purchase #7 $33.43   13.841%   $38.057   $38.06   $38.05   $38.10  
  7 purchase totals = $875.42       $943.7345   $943.73   $943.75   $943.80