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 $60.67   7.281%   $65.0874   $65.09   $65.10   $65.10  
  Purchase #2 $208.34   11.837%   $233.0012   $233.00   $233.00   $233.00  
  Purchase #3 $172.63   10.809%   $191.2896   $191.29   $191.30   $191.30  
  Purchase #4 $70.34   10.594%   $77.7918   $77.79   $77.80   $77.80  
  Purchase #5 $45.57   6.626%   $48.5895   $48.59   $48.60   $48.60  
  Purchase #6 $173.81   13.674%   $197.5768   $197.58   $197.60   $197.60  
  Purchase #7 $47.83   11.752%   $53.451   $53.45   $53.45   $53.50  
  7 purchase totals = $779.19       $866.7873   $866.79   $866.85   $866.90