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 $216.56   13.867%   $246.5904   $246.59   $246.60   $246.60  
  Purchase #2 $197.39   3.430%   $204.1605   $204.16   $204.15   $204.20  
  Purchase #3 $170.57   11.127%   $189.5493   $189.55   $189.55   $189.50  
  Purchase #4 $119.82   4.380%   $125.0681   $125.07   $125.05   $125.10  
  Purchase #5 $121.93   3.224%   $125.861   $125.86   $125.85   $125.90  
  Purchase #6 $229.58   6.506%   $244.5165   $244.52   $244.50   $244.50  
  Purchase #7 $151.99   7.500%   $163.3893   $163.39   $163.40   $163.40  
  7 purchase totals = $1,207.84       $1,299.1351   $1,299.14   $1,299.10   $1,299.20