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 $202.65   5.710%   $214.2213   $214.22   $214.20   $214.20  
  Purchase #2 $209.51   4.851%   $219.6733   $219.67   $219.65   $219.70  
  Purchase #3 $122.39   5.523%   $129.1496   $129.15   $129.15   $129.10  
  Purchase #4 $15.64   7.321%   $16.785   $16.79   $16.80   $16.80  
  Purchase #5 $218.84   11.676%   $244.3918   $244.39   $244.40   $244.40  
  Purchase #6 $6.76   11.252%   $7.5206   $7.52   $7.50   $7.50  
  Purchase #7 $200.49   13.705%   $227.9672   $227.97   $227.95   $228.00  
  7 purchase totals = $976.28       $1,059.7088   $1,059.71   $1,059.65   $1,059.70