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 $82.79   11.468%   $92.2844   $92.28   $92.30   $92.30  
  Purchase #2 $222.69   4.325%   $232.3213   $232.32   $232.30   $232.30  
  Purchase #3 $30.25   12.398%   $34.0004   $34.00   $34.00   $34.00  
  Purchase #4 $120.74   4.515%   $126.1914   $126.19   $126.20   $126.20  
  Purchase #5 $96.49   13.280%   $109.3039   $109.30   $109.30   $109.30  
  Purchase #6 $117.28   10.356%   $129.4255   $129.43   $129.45   $129.40  
  Purchase #7 $34.68   5.188%   $36.4792   $36.48   $36.50   $36.50  
  7 purchase totals = $704.92       $760.0061   $760.00   $760.05   $760.00