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 $94.46   10.413%   $104.2961   $104.30   $104.30   $104.30  
  Purchase #2 $250.38   7.731%   $269.7369   $269.74   $269.75   $269.70  
  Purchase #3 $36.62   7.515%   $39.372   $39.37   $39.35   $39.40  
  Purchase #4 $132.97   3.498%   $137.6213   $137.62   $137.60   $137.60  
  Purchase #5 $176.98   5.622%   $186.9298   $186.93   $186.95   $186.90  
  Purchase #6 $168.86   10.112%   $185.9351   $185.94   $185.95   $185.90  
  Purchase #7 $209.44   10.172%   $230.7442   $230.74   $230.75   $230.70  
  7 purchase totals = $1,069.71       $1,154.6354   $1,154.64   $1,154.65   $1,154.50