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 $206.87   13.433%   $234.6588   $234.66   $234.65   $234.70  
  Purchase #2 $100.67   5.583%   $106.2904   $106.29   $106.30   $106.30  
  Purchase #3 $160.92   12.538%   $181.0961   $181.10   $181.10   $181.10  
  Purchase #4 $28.77   5.156%   $30.2534   $30.25   $30.25   $30.30  
  Purchase #5 $119.60   7.685%   $128.7913   $128.79   $128.80   $128.80  
  Purchase #6 $72.39   4.308%   $75.5086   $75.51   $75.50   $75.50  
  Purchase #7 $44.77   9.228%   $48.9014   $48.90   $48.90   $48.90  
  7 purchase totals = $733.99       $805.5000   $805.50   $805.50   $805.60