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 $91.72   5.207%   $96.4959   $96.50   $96.50   $96.50  
  Purchase #2 $18.55   4.317%   $19.3508   $19.35   $19.35   $19.40  
  Purchase #3 $166.76   3.173%   $172.0513   $172.05   $172.05   $172.10  
  Purchase #4 $223.99   12.633%   $252.2867   $252.29   $252.30   $252.30  
  Purchase #5 $99.32   3.649%   $102.9442   $102.94   $102.95   $102.90  
  Purchase #6 $5.92   3.343%   $6.1179   $6.12   $6.10   $6.10  
  Purchase #7 $108.97   5.661%   $115.1388   $115.14   $115.15   $115.10  
  7 purchase totals = $715.23       $764.3856   $764.39   $764.40   $764.40