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 $139.34   11.219%   $154.9726   $154.97   $154.95   $155.00  
  Purchase #2 $232.43   9.597%   $254.7363   $254.74   $254.75   $254.70  
  Purchase #3 $64.95   8.701%   $70.6013   $70.60   $70.60   $70.60  
  Purchase #4 $239.94   3.740%   $248.9138   $248.91   $248.90   $248.90  
  Purchase #5 $215.92   4.548%   $225.74   $225.74   $225.75   $225.70  
  Purchase #6 $55.26   12.243%   $62.0255   $62.03   $62.05   $62.00  
  Purchase #7 $42.46   8.599%   $46.1111   $46.11   $46.10   $46.10  
  7 purchase totals = $990.30       $1,063.1006   $1,063.10   $1,063.10   $1,063.00