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 $111.82   13.463%   $126.8743   $126.87   $126.85   $126.90  
  Purchase #2 $188.58   6.858%   $201.5128   $201.51   $201.50   $201.50  
  Purchase #3 $214.98   13.831%   $244.7139   $244.71   $244.70   $244.70  
  Purchase #4 $169.35   8.113%   $183.0894   $183.09   $183.10   $183.10  
  Purchase #5 $215.50   3.623%   $223.3076   $223.31   $223.30   $223.30  
  Purchase #6 $29.29   9.725%   $32.1385   $32.14   $32.15   $32.10  
  Purchase #7 $59.92   5.588%   $63.2683   $63.27   $63.25   $63.30  
  7 purchase totals = $989.44       $1,074.9048   $1,074.90   $1,074.85   $1,074.90