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 $204.48   12.329%   $229.6903   $229.69   $229.70   $229.70  
  Purchase #2 $72.80   4.240%   $75.8867   $75.89   $75.90   $75.90  
  Purchase #3 $16.79   5.445%   $17.7042   $17.70   $17.70   $17.70  
  Purchase #4 $180.97   11.754%   $202.2412   $202.24   $202.25   $202.20  
  Purchase #5 $235.30   8.796%   $255.997   $256.00   $256.00   $256.00  
  Purchase #6 $57.87   4.540%   $60.4973   $60.50   $60.50   $60.50  
  Purchase #7 $110.93   12.726%   $125.047   $125.05   $125.05   $125.00  
  7 purchase totals = $879.14       $967.0637   $967.07   $967.10   $967.00