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 $144.61   9.225%   $157.9503   $157.95   $157.95   $158.00  
  Purchase #2 $199.66   6.608%   $212.8535   $212.85   $212.85   $212.90  
  Purchase #3 $199.58   7.391%   $214.331   $214.33   $214.35   $214.30  
  Purchase #4 $26.41   6.741%   $28.1903   $28.19   $28.20   $28.20  
  Purchase #5 $105.27   7.127%   $112.7726   $112.77   $112.75   $112.80  
  Purchase #6 $85.85   12.408%   $96.5023   $96.50   $96.50   $96.50  
  Purchase #7 $146.56   5.196%   $154.1753   $154.18   $154.20   $154.20  
  7 purchase totals = $907.94       $976.7753   $976.77   $976.80   $976.90