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 $204.97   3.656%   $212.4637   $212.46   $212.45   $212.50  
  Purchase #2 $168.97   11.688%   $188.7192   $188.72   $188.70   $188.70  
  Purchase #3 $204.42   6.640%   $217.9935   $217.99   $218.00   $218.00  
  Purchase #4 $216.77   8.181%   $234.504   $234.50   $234.50   $234.50  
  Purchase #5 $59.39   3.845%   $61.6735   $61.67   $61.65   $61.70  
  Purchase #6 $19.65   4.358%   $20.5063   $20.51   $20.50   $20.50  
  Purchase #7 $56.73   4.786%   $59.4451   $59.45   $59.45   $59.40  
  7 purchase totals = $930.90       $995.3053   $995.30   $995.25   $995.30