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 $224.62   12.787%   $253.3422   $253.34   $253.35   $253.30  
  Purchase #2 $196.53   12.654%   $221.3989   $221.40   $221.40   $221.40  
  Purchase #3 $82.55   12.407%   $92.792   $92.79   $92.80   $92.80  
  Purchase #4 $133.89   8.673%   $145.5023   $145.50   $145.50   $145.50  
  Purchase #5 $137.99   8.777%   $150.1014   $150.10   $150.10   $150.10  
  Purchase #6 $149.86   12.118%   $168.02   $168.02   $168.00   $168.00  
  Purchase #7 $14.50   5.113%   $15.2414   $15.24   $15.25   $15.20  
  7 purchase totals = $939.94       $1,046.3982   $1,046.39   $1,046.40   $1,046.30