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 $183.76   11.856%   $205.5466   $205.55   $205.55   $205.50  
  Purchase #2 $130.42   9.155%   $142.36   $142.36   $142.35   $142.40  
  Purchase #3 $190.50   5.672%   $201.3052   $201.31   $201.30   $201.30  
  Purchase #4 $139.74   8.120%   $151.0869   $151.09   $151.10   $151.10  
  Purchase #5 $84.32   6.230%   $89.5731   $89.57   $89.55   $89.60  
  Purchase #6 $8.85   11.431%   $9.8616   $9.86   $9.85   $9.90  
  Purchase #7 $229.84   6.623%   $245.0623   $245.06   $245.05   $245.10  
  7 purchase totals = $967.43       $1,044.7957   $1,044.80   $1,044.75   $1,044.90