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 $241.62   9.173%   $263.7838   $263.78   $263.80   $263.80  
  Purchase #2 $24.50   11.363%   $27.2839   $27.28   $27.30   $27.30  
  Purchase #3 $90.68   12.211%   $101.7529   $101.75   $101.75   $101.80  
  Purchase #4 $158.91   9.223%   $173.5663   $173.57   $173.55   $173.60  
  Purchase #5 $188.71   8.207%   $204.1974   $204.20   $204.20   $204.20  
  Purchase #6 $46.44   9.707%   $50.9479   $50.95   $50.95   $50.90  
  Purchase #7 $118.70   4.590%   $124.1483   $124.15   $124.15   $124.10  
  7 purchase totals = $869.56       $945.6805   $945.68   $945.70   $945.70