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 $230.93   6.704%   $246.4115   $246.41   $246.40   $246.40  
  Purchase #2 $142.98   13.268%   $161.9506   $161.95   $161.95   $162.00  
  Purchase #3 $207.62   12.777%   $234.1476   $234.15   $234.15   $234.10  
  Purchase #4 $57.88   3.226%   $59.7472   $59.75   $59.75   $59.70  
  Purchase #5 $131.81   8.823%   $143.4396   $143.44   $143.45   $143.40  
  Purchase #6 $61.29   6.568%   $65.3155   $65.32   $65.30   $65.30  
  Purchase #7 $108.31   4.611%   $113.3042   $113.30   $113.30   $113.30  
  7 purchase totals = $940.82       $1,024.3162   $1,024.32   $1,024.30   $1,024.20