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 $69.92   5.161%   $73.5286   $73.53   $73.55   $73.50  
  Purchase #2 $155.46   8.276%   $168.3259   $168.33   $168.35   $168.30  
  Purchase #3 $191.31   3.569%   $198.1379   $198.14   $198.15   $198.10  
  Purchase #4 $230.65   6.276%   $245.1256   $245.13   $245.15   $245.10  
  Purchase #5 $38.61   3.471%   $39.9502   $39.95   $39.95   $40.00  
  Purchase #6 $226.62   6.297%   $240.8903   $240.89   $240.90   $240.90  
  Purchase #7 $15.86   9.304%   $17.3356   $17.34   $17.35   $17.30  
  7 purchase totals = $928.43       $983.2941   $983.31   $983.40   $983.20