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 $244.53   5.193%   $257.2284   $257.23   $257.25   $257.20  
  Purchase #2 $111.34   11.636%   $124.2955   $124.30   $124.30   $124.30  
  Purchase #3 $181.25   9.458%   $198.3926   $198.39   $198.40   $198.40  
  Purchase #4 $205.98   6.578%   $219.5294   $219.53   $219.55   $219.50  
  Purchase #5 $162.83   8.700%   $176.9962   $177.00   $177.00   $177.00  
  Purchase #6 $244.84   6.296%   $260.2551   $260.26   $260.25   $260.30  
  Purchase #7 $131.74   7.426%   $141.523   $141.52   $141.50   $141.50  
  7 purchase totals = $1,282.51       $1,378.2202   $1,378.23   $1,378.25   $1,378.20