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 $62.65   6.537%   $66.7454   $66.75   $66.75   $66.70  
  Purchase #2 $249.56   7.202%   $267.5333   $267.53   $267.55   $267.50  
  Purchase #3 $241.61   6.454%   $257.2035   $257.20   $257.20   $257.20  
  Purchase #4 $183.75   6.469%   $195.6368   $195.64   $195.65   $195.60  
  Purchase #5 $211.37   8.869%   $230.1164   $230.12   $230.10   $230.10  
  Purchase #6 $90.77   5.334%   $95.6117   $95.61   $95.60   $95.60  
  Purchase #7 $203.88   12.863%   $230.1051   $230.11   $230.10   $230.10  
  7 purchase totals = $1,243.59       $1,342.9522   $1,342.96   $1,342.95   $1,342.80