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 $67.51   8.840%   $73.4779   $73.48   $73.50   $73.50  
  Purchase #2 $155.52   3.623%   $161.1545   $161.15   $161.15   $161.20  
  Purchase #3 $48.74   8.707%   $52.9838   $52.98   $53.00   $53.00  
  Purchase #4 $91.62   4.461%   $95.7072   $95.71   $95.70   $95.70  
  Purchase #5 $151.37   8.518%   $164.2637   $164.26   $164.25   $164.30  
  Purchase #6 $52.80   8.651%   $57.3677   $57.37   $57.35   $57.40  
  Purchase #7 $159.42   7.243%   $170.9668   $170.97   $170.95   $171.00  
  7 purchase totals = $726.98       $775.9216   $775.92   $775.90   $776.10