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 $232.61   3.614%   $241.0165   $241.02   $241.00   $241.00  
  Purchase #2 $182.38   11.702%   $203.7221   $203.72   $203.70   $203.70  
  Purchase #3 $165.33   13.250%   $187.2362   $187.24   $187.25   $187.20  
  Purchase #4 $127.25   4.317%   $132.7434   $132.74   $132.75   $132.70  
  Purchase #5 $50.26   13.498%   $57.0441   $57.04   $57.05   $57.00  
  Purchase #6 $75.90   3.656%   $78.6749   $78.67   $78.65   $78.70  
  Purchase #7 $8.54   7.312%   $9.1644   $9.16   $9.15   $9.20  
  7 purchase totals = $842.27       $909.6016   $909.59   $909.55   $909.50