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 $66.74   9.671%   $73.1944   $73.19   $73.20   $73.20  
  Purchase #2 $228.25   8.197%   $246.9597   $246.96   $246.95   $247.00  
  Purchase #3 $57.99   7.483%   $62.3294   $62.33   $62.35   $62.30  
  Purchase #4 $212.84   11.183%   $236.6419   $236.64   $236.65   $236.60  
  Purchase #5 $42.29   7.873%   $45.6195   $45.62   $45.60   $45.60  
  Purchase #6 $187.39   4.501%   $195.8244   $195.82   $195.80   $195.80  
  Purchase #7 $49.45   12.545%   $55.6535   $55.65   $55.65   $55.70  
  7 purchase totals = $844.95       $916.2228   $916.21   $916.20   $916.20