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 $67.29   13.210%   $76.179   $76.18   $76.20   $76.20  
  Purchase #2 $137.27   13.532%   $155.8454   $155.85   $155.85   $155.80  
  Purchase #3 $153.34   4.788%   $160.6819   $160.68   $160.70   $160.70  
  Purchase #4 $43.47   10.226%   $47.9152   $47.92   $47.90   $47.90  
  Purchase #5 $69.79   4.614%   $73.0101   $73.01   $73.00   $73.00  
  Purchase #6 $164.31   12.256%   $184.4478   $184.45   $184.45   $184.40  
  Purchase #7 $161.29   7.829%   $173.9174   $173.92   $173.90   $173.90  
  7 purchase totals = $796.76       $871.9968   $872.01   $872.00   $871.90