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 $66.81   6.177%   $70.9369   $70.94   $70.95   $70.90  
  Purchase #2 $127.29   11.358%   $141.7476   $141.75   $141.75   $141.70  
  Purchase #3 $111.55   12.633%   $125.6421   $125.64   $125.65   $125.60  
  Purchase #4 $141.47   6.693%   $150.9386   $150.94   $150.95   $150.90  
  Purchase #5 $87.61   6.116%   $92.9682   $92.97   $92.95   $93.00  
  Purchase #6 $109.97   6.871%   $117.526   $117.53   $117.55   $117.50  
  Purchase #7 $60.70   8.648%   $65.9493   $65.95   $65.95   $65.90  
  7 purchase totals = $705.40       $765.7087   $765.72   $765.75   $765.50