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 $168.70   9.121%   $184.0871   $184.09   $184.10   $184.10  
  Purchase #2 $144.61   13.288%   $163.8258   $163.83   $163.85   $163.80  
  Purchase #3 $60.94   7.601%   $65.572   $65.57   $65.55   $65.60  
  Purchase #4 $69.62   5.246%   $73.2723   $73.27   $73.25   $73.30  
  Purchase #5 $224.94   8.182%   $243.3446   $243.34   $243.35   $243.30  
  Purchase #6 $119.93   13.223%   $135.7883   $135.79   $135.80   $135.80  
  Purchase #7 $148.87   8.314%   $161.2471   $161.25   $161.25   $161.20  
  7 purchase totals = $937.61       $1,027.1372   $1,027.14   $1,027.15   $1,027.10