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 $55.87   11.212%   $62.1341   $62.13   $62.15   $62.10  
  Purchase #2 $194.79   13.395%   $220.8821   $220.88   $220.90   $220.90  
  Purchase #3 $35.89   7.539%   $38.5957   $38.60   $38.60   $38.60  
  Purchase #4 $84.55   6.766%   $90.2707   $90.27   $90.25   $90.30  
  Purchase #5 $241.73   11.137%   $268.6515   $268.65   $268.65   $268.70  
  Purchase #6 $248.26   6.804%   $265.1516   $265.15   $265.15   $265.20  
  Purchase #7 $163.39   10.759%   $180.9691   $180.97   $180.95   $181.00  
  7 purchase totals = $1,024.48       $1,126.6548   $1,126.65   $1,126.65   $1,126.80