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 $224.72   11.787%   $251.2077   $251.21   $251.20   $251.20  
  Purchase #2 $145.69   8.796%   $158.5049   $158.50   $158.50   $158.50  
  Purchase #3 $178.85   10.587%   $197.7848   $197.78   $197.80   $197.80  
  Purchase #4 $22.88   4.719%   $23.9597   $23.96   $23.95   $24.00  
  Purchase #5 $103.62   13.751%   $117.8688   $117.87   $117.85   $117.90  
  Purchase #6 $95.68   6.614%   $102.0083   $102.01   $102.00   $102.00  
  Purchase #7 $110.42   7.697%   $118.919   $118.92   $118.90   $118.90  
  7 purchase totals = $881.86       $970.2532   $970.25   $970.20   $970.30