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 $184.86   12.372%   $207.7309   $207.73   $207.75   $207.70  
  Purchase #2 $38.82   7.278%   $41.6453   $41.65   $41.65   $41.60  
  Purchase #3 $169.89   6.241%   $180.4928   $180.49   $180.50   $180.50  
  Purchase #4 $112.74   12.822%   $127.1955   $127.20   $127.20   $127.20  
  Purchase #5 $79.58   11.758%   $88.937   $88.94   $88.95   $88.90  
  Purchase #6 $211.88   13.657%   $240.8165   $240.82   $240.80   $240.80  
  Purchase #7 $182.90   6.825%   $195.3829   $195.38   $195.40   $195.40  
  7 purchase totals = $980.67       $1,082.2009   $1,082.21   $1,082.25   $1,082.10