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 $44.82   11.615%   $50.0258   $50.03   $50.05   $50.00  
  Purchase #2 $153.35   10.459%   $169.3889   $169.39   $169.40   $169.40  
  Purchase #3 $9.85   11.150%   $10.9483   $10.95   $10.95   $10.90  
  Purchase #4 $182.68   4.769%   $191.392   $191.39   $191.40   $191.40  
  Purchase #5 $177.91   13.256%   $201.4937   $201.49   $201.50   $201.50  
  Purchase #6 $159.93   10.256%   $176.3324   $176.33   $176.35   $176.30  
  Purchase #7 $230.81   12.503%   $259.6682   $259.67   $259.65   $259.70  
  7 purchase totals = $959.35       $1,059.2493   $1,059.25   $1,059.30   $1,059.20