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 $58.87   4.173%   $61.3266   $61.33   $61.35   $61.30  
  Purchase #2 $198.32   7.264%   $212.726   $212.73   $212.75   $212.70  
  Purchase #3 $15.93   8.253%   $17.2447   $17.24   $17.25   $17.20  
  Purchase #4 $233.90   13.137%   $264.6274   $264.63   $264.65   $264.60  
  Purchase #5 $155.59   5.536%   $164.2035   $164.20   $164.20   $164.20  
  Purchase #6 $10.77   6.738%   $11.4957   $11.50   $11.50   $11.50  
  Purchase #7 $222.25   6.641%   $237.0096   $237.01   $237.00   $237.00  
  7 purchase totals = $895.63       $968.6335   $968.64   $968.70   $968.50