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 $83.37   5.558%   $88.0037   $88.00   $88.00   $88.00  
  Purchase #2 $91.98   12.719%   $103.6789   $103.68   $103.70   $103.70  
  Purchase #3 $115.82   8.818%   $126.033   $126.03   $126.05   $126.00  
  Purchase #4 $115.82   11.463%   $129.0964   $129.10   $129.10   $129.10  
  Purchase #5 $44.98   6.761%   $48.0211   $48.02   $48.00   $48.00  
  Purchase #6 $134.27   4.140%   $139.8288   $139.83   $139.85   $139.80  
  Purchase #7 $167.50   5.482%   $176.6824   $176.68   $176.70   $176.70  
  7 purchase totals = $753.74       $811.3443   $811.34   $811.40   $811.30