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 $81.59   13.333%   $92.4684   $92.47   $92.45   $92.50  
  Purchase #2 $241.39   3.154%   $249.0034   $249.00   $249.00   $249.00  
  Purchase #3 $168.30   10.254%   $185.5575   $185.56   $185.55   $185.60  
  Purchase #4 $71.79   4.675%   $75.1462   $75.15   $75.15   $75.10  
  Purchase #5 $185.51   7.505%   $199.4325   $199.43   $199.45   $199.40  
  Purchase #6 $165.31   10.518%   $182.6973   $182.70   $182.70   $182.70  
  Purchase #7 $50.87   11.853%   $56.8996   $56.90   $56.90   $56.90  
  7 purchase totals = $964.76       $1,041.2049   $1,041.21   $1,041.20   $1,041.20