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 $191.94   7.830%   $206.9689   $206.97   $206.95   $207.00  
  Purchase #2 $56.77   8.607%   $61.6562   $61.66   $61.65   $61.70  
  Purchase #3 $11.25   11.390%   $12.5314   $12.53   $12.55   $12.50  
  Purchase #4 $104.84   12.266%   $117.6997   $117.70   $117.70   $117.70  
  Purchase #5 $211.81   9.514%   $231.9616   $231.96   $231.95   $232.00  
  Purchase #6 $200.80   10.254%   $221.39   $221.39   $221.40   $221.40  
  Purchase #7 $77.89   3.413%   $80.5484   $80.55   $80.55   $80.50  
  7 purchase totals = $855.30       $932.7562   $932.76   $932.75   $932.80