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 $44.60   8.239%   $48.2746   $48.27   $48.25   $48.30  
  Purchase #2 $113.85   11.347%   $126.7686   $126.77   $126.75   $126.80  
  Purchase #3 $27.35   8.148%   $29.5785   $29.58   $29.60   $29.60  
  Purchase #4 $9.41   8.551%   $10.2146   $10.21   $10.20   $10.20  
  Purchase #5 $214.52   10.826%   $237.7439   $237.74   $237.75   $237.70  
  Purchase #6 $238.97   8.497%   $259.2753   $259.28   $259.30   $259.30  
  Purchase #7 $37.77   6.586%   $40.2575   $40.26   $40.25   $40.30  
  7 purchase totals = $686.47       $752.1130   $752.11   $752.10   $752.20