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 $88.45   5.331%   $93.1653   $93.17   $93.15   $93.20  
  Purchase #2 $207.35   4.793%   $217.2883   $217.29   $217.30   $217.30  
  Purchase #3 $218.99   12.459%   $246.274   $246.27   $246.25   $246.30  
  Purchase #4 $171.42   9.678%   $188.01   $188.01   $188.00   $188.00  
  Purchase #5 $116.97   6.265%   $124.2982   $124.30   $124.30   $124.30  
  Purchase #6 $34.45   11.549%   $38.4286   $38.43   $38.45   $38.40  
  Purchase #7 $43.68   13.707%   $49.6672   $49.67   $49.65   $49.70  
  7 purchase totals = $881.31       $957.1316   $957.14   $957.10   $957.20