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 $61.79   10.659%   $68.3762   $68.38   $68.40   $68.40  
  Purchase #2 $208.61   8.868%   $227.1095   $227.11   $227.10   $227.10  
  Purchase #3 $70.90   8.128%   $76.6628   $76.66   $76.65   $76.70  
  Purchase #4 $249.33   7.528%   $268.0996   $268.10   $268.10   $268.10  
  Purchase #5 $215.94   8.141%   $233.5197   $233.52   $233.50   $233.50  
  Purchase #6 $216.80   10.278%   $239.0827   $239.08   $239.10   $239.10  
  Purchase #7 $69.60   11.632%   $77.6959   $77.70   $77.70   $77.70  
  7 purchase totals = $1,092.97       $1,190.5464   $1,190.55   $1,190.55   $1,190.60