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 $249.75   9.640%   $273.8259   $273.83   $273.85   $273.80  
  Purchase #2 $59.46   3.112%   $61.3104   $61.31   $61.30   $61.30  
  Purchase #3 $150.70   4.301%   $157.1816   $157.18   $157.20   $157.20  
  Purchase #4 $213.36   9.685%   $234.0239   $234.02   $234.00   $234.00  
  Purchase #5 $144.63   5.280%   $152.2665   $152.27   $152.25   $152.30  
  Purchase #6 $173.55   13.418%   $196.8369   $196.84   $196.85   $196.80  
  Purchase #7 $111.34   13.778%   $126.6804   $126.68   $126.70   $126.70  
  7 purchase totals = $1,102.79       $1,202.1256   $1,202.13   $1,202.15   $1,202.10