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 $60.96   4.279%   $63.5685   $63.57   $63.55   $63.60  
  Purchase #2 $19.73   5.286%   $20.7729   $20.77   $20.75   $20.80  
  Purchase #3 $241.93   10.281%   $266.8028   $266.80   $266.80   $266.80  
  Purchase #4 $26.30   5.689%   $27.7962   $27.80   $27.80   $27.80  
  Purchase #5 $119.26   7.297%   $127.9624   $127.96   $127.95   $128.00  
  Purchase #6 $136.26   6.703%   $145.3935   $145.39   $145.40   $145.40  
  Purchase #7 $190.48   7.689%   $205.126   $205.13   $205.15   $205.10  
  7 purchase totals = $794.92       $857.4223   $857.42   $857.40   $857.50