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 $204.89   8.496%   $222.2975   $222.30   $222.30   $222.30  
  Purchase #2 $66.48   7.341%   $71.3603   $71.36   $71.35   $71.40  
  Purchase #3 $242.90   4.751%   $254.4402   $254.44   $254.45   $254.40  
  Purchase #4 $71.34   13.473%   $80.9516   $80.95   $80.95   $81.00  
  Purchase #5 $159.65   11.442%   $177.9172   $177.92   $177.90   $177.90  
  Purchase #6 $133.27   11.655%   $148.8026   $148.80   $148.80   $148.80  
  Purchase #7 $55.57   5.113%   $58.4113   $58.41   $58.40   $58.40  
  7 purchase totals = $934.10       $1,014.1807   $1,014.18   $1,014.15   $1,014.20