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 $86.37   7.634%   $92.9635   $92.96   $92.95   $93.00  
  Purchase #2 $57.60   12.617%   $64.8674   $64.87   $64.85   $64.90  
  Purchase #3 $55.28   4.475%   $57.7538   $57.75   $57.75   $57.80  
  Purchase #4 $56.65   13.670%   $64.3941   $64.39   $64.40   $64.40  
  Purchase #5 $197.48   8.651%   $214.564   $214.56   $214.55   $214.60  
  Purchase #6 $244.27   13.566%   $277.4077   $277.41   $277.40   $277.40  
  Purchase #7 $189.30   12.270%   $212.5271   $212.53   $212.55   $212.50  
  7 purchase totals = $886.95       $984.4776   $984.47   $984.45   $984.60