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 $242.53   8.789%   $263.846   $263.85   $263.85   $263.80  
  Purchase #2 $102.53   3.717%   $106.341   $106.34   $106.35   $106.30  
  Purchase #3 $125.95   12.616%   $141.8399   $141.84   $141.85   $141.80  
  Purchase #4 $226.63   12.660%   $255.3214   $255.32   $255.30   $255.30  
  Purchase #5 $249.91   3.599%   $258.9043   $258.90   $258.90   $258.90  
  Purchase #6 $145.78   9.494%   $159.6204   $159.62   $159.60   $159.60  
  Purchase #7 $71.91   7.713%   $77.4564   $77.46   $77.45   $77.50  
  7 purchase totals = $1,165.24       $1,263.3294   $1,263.33   $1,263.30   $1,263.20