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 $189.95   7.705%   $204.5856   $204.59   $204.60   $204.60  
  Purchase #2 $223.91   7.119%   $239.8502   $239.85   $239.85   $239.90  
  Purchase #3 $64.55   3.356%   $66.7163   $66.72   $66.70   $66.70  
  Purchase #4 $205.34   6.612%   $218.9171   $218.92   $218.90   $218.90  
  Purchase #5 $108.83   6.863%   $116.299   $116.30   $116.30   $116.30  
  Purchase #6 $48.64   6.719%   $51.9081   $51.91   $51.90   $51.90  
  Purchase #7 $85.34   3.319%   $88.1724   $88.17   $88.15   $88.20  
  7 purchase totals = $926.56       $986.4487   $986.46   $986.40   $986.50