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 $112.34   11.288%   $125.0209   $125.02   $125.00   $125.00  
  Purchase #2 $187.88   10.119%   $206.8916   $206.89   $206.90   $206.90  
  Purchase #3 $132.60   6.227%   $140.857   $140.86   $140.85   $140.90  
  Purchase #4 $8.28   11.720%   $9.2504   $9.25   $9.25   $9.30  
  Purchase #5 $98.32   5.119%   $103.353   $103.35   $103.35   $103.40  
  Purchase #6 $61.45   7.358%   $65.9715   $65.97   $65.95   $66.00  
  Purchase #7 $215.41   4.603%   $225.3253   $225.33   $225.35   $225.30  
  7 purchase totals = $816.28       $876.6697   $876.67   $876.65   $876.80