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 $7.89   7.669%   $8.4951   $8.50   $8.50   $8.50  
  Purchase #2 $131.71   9.750%   $144.5517   $144.55   $144.55   $144.60  
  Purchase #3 $177.82   9.280%   $194.3217   $194.32   $194.30   $194.30  
  Purchase #4 $157.75   9.808%   $173.2221   $173.22   $173.20   $173.20  
  Purchase #5 $209.67   3.433%   $216.868   $216.87   $216.85   $216.90  
  Purchase #6 $170.73   3.301%   $176.3658   $176.37   $176.35   $176.40  
  Purchase #7 $189.92   3.253%   $196.0981   $196.10   $196.10   $196.10  
  7 purchase totals = $1,045.49       $1,109.9225   $1,109.93   $1,109.85   $1,110.00