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 $214.32   5.818%   $226.7891   $226.79   $226.80   $226.80  
  Purchase #2 $79.37   9.109%   $86.5998   $86.60   $86.60   $86.60  
  Purchase #3 $5.96   11.594%   $6.651   $6.65   $6.65   $6.70  
  Purchase #4 $95.88   7.129%   $102.7153   $102.72   $102.70   $102.70  
  Purchase #5 $69.97   9.337%   $76.5031   $76.50   $76.50   $76.50  
  Purchase #6 $181.30   13.762%   $206.2505   $206.25   $206.25   $206.30  
  Purchase #7 $50.91   9.697%   $55.8467   $55.85   $55.85   $55.80  
  7 purchase totals = $697.71       $761.3555   $761.36   $761.35   $761.40