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 $119.66   6.407%   $127.3266   $127.33   $127.35   $127.30  
  Purchase #2 $84.97   10.640%   $94.0108   $94.01   $94.00   $94.00  
  Purchase #3 $224.39   9.458%   $245.6128   $245.61   $245.60   $245.60  
  Purchase #4 $135.77   5.557%   $143.3147   $143.31   $143.30   $143.30  
  Purchase #5 $244.42   12.205%   $274.2515   $274.25   $274.25   $274.30  
  Purchase #6 $155.39   6.670%   $165.7545   $165.75   $165.75   $165.80  
  Purchase #7 $238.37   9.644%   $261.3584   $261.36   $261.35   $261.40  
  7 purchase totals = $1,202.97       $1,311.6293   $1,311.62   $1,311.60   $1,311.70