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 $54.55   8.532%   $59.2042   $59.20   $59.20   $59.20  
  Purchase #2 $72.83   11.710%   $81.3584   $81.36   $81.35   $81.40  
  Purchase #3 $217.29   13.674%   $247.0022   $247.00   $247.00   $247.00  
  Purchase #4 $206.61   12.454%   $232.3412   $232.34   $232.35   $232.30  
  Purchase #5 $88.77   8.459%   $96.2791   $96.28   $96.30   $96.30  
  Purchase #6 $247.26   9.800%   $271.4915   $271.49   $271.50   $271.50  
  Purchase #7 $172.53   6.802%   $184.2655   $184.27   $184.25   $184.30  
  7 purchase totals = $1,059.84       $1,171.9421   $1,171.94   $1,171.95   $1,172.00