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 $148.52   10.824%   $164.5958   $164.60   $164.60   $164.60  
  Purchase #2 $215.53   11.290%   $239.8633   $239.86   $239.85   $239.90  
  Purchase #3 $85.34   13.616%   $96.9599   $96.96   $96.95   $97.00  
  Purchase #4 $208.93   11.157%   $232.2403   $232.24   $232.25   $232.20  
  Purchase #5 $166.99   11.137%   $185.5877   $185.59   $185.60   $185.60  
  Purchase #6 $143.91   5.488%   $151.8078   $151.81   $151.80   $151.80  
  Purchase #7 $241.96   7.820%   $260.8813   $260.88   $260.90   $260.90  
  7 purchase totals = $1,211.18       $1,331.9361   $1,331.94   $1,331.95   $1,332.00