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 $193.45   7.636%   $208.2218   $208.22   $208.20   $208.20  
  Purchase #2 $61.40   3.357%   $63.4612   $63.46   $63.45   $63.50  
  Purchase #3 $26.80   9.480%   $29.3406   $29.34   $29.35   $29.30  
  Purchase #4 $63.82   7.358%   $68.5159   $68.52   $68.50   $68.50  
  Purchase #5 $119.74   6.572%   $127.6093   $127.61   $127.60   $127.60  
  Purchase #6 $107.41   11.602%   $119.8717   $119.87   $119.85   $119.90  
  Purchase #7 $148.37   4.834%   $155.5422   $155.54   $155.55   $155.50  
  7 purchase totals = $720.99       $772.5627   $772.56   $772.50   $772.50