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 $202.50   13.861%   $230.5685   $230.57   $230.55   $230.60  
  Purchase #2 $92.77   5.306%   $97.6924   $97.69   $97.70   $97.70  
  Purchase #3 $224.33   7.847%   $241.9332   $241.93   $241.95   $241.90  
  Purchase #4 $103.41   6.223%   $109.8452   $109.85   $109.85   $109.80  
  Purchase #5 $241.50   6.573%   $257.3738   $257.37   $257.35   $257.40  
  Purchase #6 $76.37   11.696%   $85.3022   $85.30   $85.30   $85.30  
  Purchase #7 $39.29   13.464%   $44.58   $44.58   $44.60   $44.60  
  7 purchase totals = $980.17       $1,067.2953   $1,067.29   $1,067.30   $1,067.30