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 $39.82   8.189%   $43.0809   $43.08   $43.10   $43.10  
  Purchase #2 $222.34   3.345%   $229.7773   $229.78   $229.80   $229.80  
  Purchase #3 $133.83   11.476%   $149.1883   $149.19   $149.20   $149.20  
  Purchase #4 $55.43   11.512%   $61.8111   $61.81   $61.80   $61.80  
  Purchase #5 $22.46   6.652%   $23.954   $23.95   $23.95   $24.00  
  Purchase #6 $33.44   12.366%   $37.5752   $37.58   $37.60   $37.60  
  Purchase #7 $211.87   7.254%   $227.239   $227.24   $227.25   $227.20  
  7 purchase totals = $719.19       $772.6258   $772.63   $772.70   $772.70