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 $221.39   8.263%   $239.6835   $239.68   $239.70   $239.70  
  Purchase #2 $173.96   12.471%   $195.6546   $195.65   $195.65   $195.70  
  Purchase #3 $68.53   13.541%   $77.8096   $77.81   $77.80   $77.80  
  Purchase #4 $105.65   12.636%   $118.9999   $119.00   $119.00   $119.00  
  Purchase #5 $144.29   7.800%   $155.5446   $155.54   $155.55   $155.50  
  Purchase #6 $144.59   12.791%   $163.0845   $163.08   $163.10   $163.10  
  Purchase #7 $244.41   13.657%   $277.7891   $277.79   $277.80   $277.80  
  7 purchase totals = $1,102.82       $1,228.5658   $1,228.55   $1,228.60   $1,228.60