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 $55.59   11.852%   $62.1785   $62.18   $62.20   $62.20  
  Purchase #2 $93.54   10.496%   $103.358   $103.36   $103.35   $103.40  
  Purchase #3 $65.43   10.277%   $72.1542   $72.15   $72.15   $72.20  
  Purchase #4 $100.52   4.704%   $105.2485   $105.25   $105.25   $105.20  
  Purchase #5 $219.51   11.189%   $244.071   $244.07   $244.05   $244.10  
  Purchase #6 $24.84   7.851%   $26.7902   $26.79   $26.80   $26.80  
  Purchase #7 $202.78   5.531%   $213.9958   $214.00   $214.00   $214.00  
  7 purchase totals = $762.21       $827.7962   $827.80   $827.80   $827.90