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 $168.29   9.681%   $184.5822   $184.58   $184.60   $184.60  
  Purchase #2 $68.75   8.157%   $74.3579   $74.36   $74.35   $74.40  
  Purchase #3 $118.79   6.382%   $126.3712   $126.37   $126.35   $126.40  
  Purchase #4 $61.26   11.166%   $68.1003   $68.10   $68.10   $68.10  
  Purchase #5 $169.86   4.178%   $176.9568   $176.96   $176.95   $177.00  
  Purchase #6 $201.40   9.541%   $220.6156   $220.62   $220.60   $220.60  
  Purchase #7 $175.85   10.327%   $194.01   $194.01   $194.00   $194.00  
  7 purchase totals = $964.20       $1,044.9940   $1,045.00   $1,044.95   $1,045.10