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 $79.40   7.683%   $85.5003   $85.50   $85.50   $85.50  
  Purchase #2 $186.96   6.255%   $198.6543   $198.65   $198.65   $198.70  
  Purchase #3 $112.51   4.832%   $117.9465   $117.95   $117.95   $117.90  
  Purchase #4 $233.51   4.215%   $243.3524   $243.35   $243.35   $243.40  
  Purchase #5 $104.41   12.444%   $117.4028   $117.40   $117.40   $117.40  
  Purchase #6 $47.79   9.613%   $52.3841   $52.38   $52.40   $52.40  
  Purchase #7 $180.50   8.363%   $195.5952   $195.60   $195.60   $195.60  
  7 purchase totals = $945.08       $1,010.8356   $1,010.83   $1,010.85   $1,010.90