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 $214.76   7.724%   $231.3481   $231.35   $231.35   $231.30  
  Purchase #2 $53.76   9.641%   $58.943   $58.94   $58.95   $58.90  
  Purchase #3 $206.42   8.333%   $223.621   $223.62   $223.60   $223.60  
  Purchase #4 $115.72   7.769%   $124.7103   $124.71   $124.70   $124.70  
  Purchase #5 $244.77   11.502%   $272.9234   $272.92   $272.90   $272.90  
  Purchase #6 $130.34   4.593%   $136.3265   $136.33   $136.35   $136.30  
  Purchase #7 $118.29   7.253%   $126.8696   $126.87   $126.85   $126.90  
  7 purchase totals = $1,084.06       $1,174.7419   $1,174.74   $1,174.70   $1,174.60