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 $158.47   11.662%   $176.9508   $176.95   $176.95   $177.00  
  Purchase #2 $59.99   8.803%   $65.2709   $65.27   $65.25   $65.30  
  Purchase #3 $213.83   11.442%   $238.2964   $238.30   $238.30   $238.30  
  Purchase #4 $48.53   6.833%   $51.8461   $51.85   $51.85   $51.80  
  Purchase #5 $248.62   8.827%   $270.5657   $270.57   $270.55   $270.60  
  Purchase #6 $15.40   12.657%   $17.3492   $17.35   $17.35   $17.30  
  Purchase #7 $120.37   12.535%   $135.4584   $135.46   $135.45   $135.50  
  7 purchase totals = $865.21       $955.7375   $955.75   $955.70   $955.80