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 $222.54   10.574%   $246.0714   $246.07   $246.05   $246.10  
  Purchase #2 $199.26   4.619%   $208.4638   $208.46   $208.45   $208.50  
  Purchase #3 $210.90   13.127%   $238.5848   $238.58   $238.60   $238.60  
  Purchase #4 $223.39   10.447%   $246.7276   $246.73   $246.75   $246.70  
  Purchase #5 $68.93   7.480%   $74.086   $74.09   $74.10   $74.10  
  Purchase #6 $100.45   13.372%   $113.8822   $113.88   $113.90   $113.90  
  Purchase #7 $230.43   3.854%   $239.3108   $239.31   $239.30   $239.30  
  7 purchase totals = $1,255.90       $1,367.1266   $1,367.12   $1,367.15   $1,367.20