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 $174.87   11.627%   $195.2021   $195.20   $195.20   $195.20  
  Purchase #2 $207.58   6.149%   $220.3441   $220.34   $220.35   $220.30  
  Purchase #3 $237.63   9.564%   $260.3569   $260.36   $260.35   $260.40  
  Purchase #4 $101.98   8.844%   $110.9991   $111.00   $111.00   $111.00  
  Purchase #5 $82.38   10.688%   $91.1848   $91.18   $91.20   $91.20  
  Purchase #6 $13.98   10.450%   $15.4409   $15.44   $15.45   $15.40  
  Purchase #7 $246.53   13.234%   $279.1558   $279.16   $279.15   $279.20  
  7 purchase totals = $1,064.95       $1,172.6837   $1,172.68   $1,172.70   $1,172.70