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 $94.83   4.756%   $99.3401   $99.34   $99.35   $99.30  
  Purchase #2 $71.79   13.776%   $81.6798   $81.68   $81.70   $81.70  
  Purchase #3 $154.93   4.572%   $162.0134   $162.01   $162.00   $162.00  
  Purchase #4 $20.60   4.392%   $21.5048   $21.50   $21.50   $21.50  
  Purchase #5 $201.56   12.249%   $226.2491   $226.25   $226.25   $226.20  
  Purchase #6 $99.61   13.774%   $113.3303   $113.33   $113.35   $113.30  
  Purchase #7 $225.97   11.347%   $251.6108   $251.61   $251.60   $251.60  
  7 purchase totals = $869.29       $955.7283   $955.72   $955.75   $955.60