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 $115.27   8.467%   $125.0299   $125.03   $125.05   $125.00  
  Purchase #2 $25.71   4.796%   $26.9431   $26.94   $26.95   $26.90  
  Purchase #3 $20.36   8.558%   $22.1024   $22.10   $22.10   $22.10  
  Purchase #4 $202.33   5.398%   $213.2518   $213.25   $213.25   $213.30  
  Purchase #5 $33.35   8.334%   $36.1294   $36.13   $36.15   $36.10  
  Purchase #6 $191.73   6.655%   $204.4896   $204.49   $204.50   $204.50  
  Purchase #7 $123.99   5.714%   $131.0748   $131.07   $131.05   $131.10  
  7 purchase totals = $712.74       $759.0210   $759.01   $759.05   $759.00