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 $96.39   7.683%   $103.7956   $103.80   $103.80   $103.80  
  Purchase #2 $29.86   5.842%   $31.6044   $31.60   $31.60   $31.60  
  Purchase #3 $185.57   3.684%   $192.4064   $192.41   $192.40   $192.40  
  Purchase #4 $232.30   4.692%   $243.1995   $243.20   $243.20   $243.20  
  Purchase #5 $237.83   4.722%   $249.0603   $249.06   $249.05   $249.10  
  Purchase #6 $84.72   12.478%   $95.2914   $95.29   $95.30   $95.30  
  Purchase #7 $41.98   13.449%   $47.6259   $47.63   $47.65   $47.60  
  7 purchase totals = $908.65       $962.9835   $962.99   $963.00   $963.00