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 $219.45   10.557%   $242.6173   $242.62   $242.60   $242.60  
  Purchase #2 $234.89   8.650%   $255.208   $255.21   $255.20   $255.20  
  Purchase #3 $17.88   4.476%   $18.6803   $18.68   $18.70   $18.70  
  Purchase #4 $82.29   5.141%   $86.5205   $86.52   $86.50   $86.50  
  Purchase #5 $23.90   9.230%   $26.106   $26.11   $26.10   $26.10  
  Purchase #6 $237.68   3.473%   $245.9346   $245.93   $245.95   $245.90  
  Purchase #7 $70.81   4.518%   $74.0092   $74.01   $74.00   $74.00  
  7 purchase totals = $886.90       $949.0759   $949.08   $949.05   $949.00