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 $189.79   6.457%   $202.0447   $202.04   $202.05   $202.00  
  Purchase #2 $248.93   11.494%   $277.542   $277.54   $277.55   $277.50  
  Purchase #3 $85.55   11.805%   $95.6492   $95.65   $95.65   $95.60  
  Purchase #4 $127.62   13.229%   $144.5028   $144.50   $144.50   $144.50  
  Purchase #5 $6.34   5.779%   $6.7064   $6.71   $6.70   $6.70  
  Purchase #6 $78.80   13.103%   $89.1252   $89.13   $89.15   $89.10  
  Purchase #7 $195.96   6.129%   $207.9704   $207.97   $207.95   $208.00  
  7 purchase totals = $932.99       $1,023.5407   $1,023.54   $1,023.55   $1,023.40