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 $195.69   12.524%   $220.1982   $220.20   $220.20   $220.20  
  Purchase #2 $141.77   8.854%   $154.3223   $154.32   $154.30   $154.30  
  Purchase #3 $20.52   13.863%   $23.3647   $23.36   $23.35   $23.40  
  Purchase #4 $222.65   11.354%   $247.9297   $247.93   $247.95   $247.90  
  Purchase #5 $144.42   3.629%   $149.661   $149.66   $149.65   $149.70  
  Purchase #6 $212.88   7.446%   $228.731   $228.73   $228.75   $228.70  
  Purchase #7 $194.68   6.851%   $208.0175   $208.02   $208.00   $208.00  
  7 purchase totals = $1,132.61       $1,232.2244   $1,232.22   $1,232.20   $1,232.20