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 $56.94   5.656%   $60.1605   $60.16   $60.15   $60.20  
  Purchase #2 $95.34   9.480%   $104.3782   $104.38   $104.40   $104.40  
  Purchase #3 $111.37   8.200%   $120.5023   $120.50   $120.50   $120.50  
  Purchase #4 $55.70   5.477%   $58.7507   $58.75   $58.75   $58.80  
  Purchase #5 $51.37   5.830%   $54.3649   $54.36   $54.35   $54.40  
  Purchase #6 $128.60   9.853%   $141.271   $141.27   $141.25   $141.30  
  Purchase #7 $153.67   11.523%   $171.3774   $171.38   $171.40   $171.40  
  7 purchase totals = $652.99       $710.8050   $710.80   $710.80   $711.00