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 $87.86   9.752%   $96.4281   $96.43   $96.45   $96.40  
  Purchase #2 $15.56   12.424%   $17.4932   $17.49   $17.50   $17.50  
  Purchase #3 $203.80   4.509%   $212.9893   $212.99   $213.00   $213.00  
  Purchase #4 $28.98   10.352%   $31.98   $31.98   $32.00   $32.00  
  Purchase #5 $65.93   7.164%   $70.6532   $70.65   $70.65   $70.70  
  Purchase #6 $84.56   5.263%   $89.0104   $89.01   $89.00   $89.00  
  Purchase #7 $92.61   11.632%   $103.3824   $103.38   $103.40   $103.40  
  7 purchase totals = $579.30       $621.9366   $621.93   $622.00   $622.00