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 $52.57   11.339%   $58.5309   $58.53   $58.55   $58.50  
  Purchase #2 $230.64   8.791%   $250.9156   $250.92   $250.90   $250.90  
  Purchase #3 $67.44   3.451%   $69.7674   $69.77   $69.75   $69.80  
  Purchase #4 $182.32   4.253%   $190.0741   $190.07   $190.05   $190.10  
  Purchase #5 $166.68   5.851%   $176.4324   $176.43   $176.45   $176.40  
  Purchase #6 $98.68   5.284%   $103.8943   $103.89   $103.90   $103.90  
  Purchase #7 $25.37   6.483%   $27.0147   $27.01   $27.00   $27.00  
  7 purchase totals = $823.70       $876.6294   $876.62   $876.60   $876.60