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 $73.58   8.418%   $79.774   $79.77   $79.75   $79.80  
  Purchase #2 $224.63   7.116%   $240.6147   $240.61   $240.60   $240.60  
  Purchase #3 $156.68   4.511%   $163.7478   $163.75   $163.75   $163.70  
  Purchase #4 $147.28   13.429%   $167.0582   $167.06   $167.05   $167.10  
  Purchase #5 $92.86   7.367%   $99.701   $99.70   $99.70   $99.70  
  Purchase #6 $217.59   11.584%   $242.7956   $242.80   $242.80   $242.80  
  Purchase #7 $49.99   5.117%   $52.548   $52.55   $52.55   $52.50  
  7 purchase totals = $962.61       $1,046.2393   $1,046.24   $1,046.20   $1,046.20