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 $94.67   13.169%   $107.1371   $107.14   $107.15   $107.10  
  Purchase #2 $40.86   13.400%   $46.3352   $46.34   $46.35   $46.30  
  Purchase #3 $50.26   3.517%   $52.0276   $52.03   $52.05   $52.00  
  Purchase #4 $151.28   10.380%   $166.9829   $166.98   $167.00   $167.00  
  Purchase #5 $236.78   7.722%   $255.0642   $255.06   $255.05   $255.10  
  Purchase #6 $135.78   11.648%   $151.5957   $151.60   $151.60   $151.60  
  Purchase #7 $244.86   3.628%   $253.7435   $253.74   $253.75   $253.70  
  7 purchase totals = $954.49       $1,032.8862   $1,032.89   $1,032.95   $1,032.80