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 $216.94   7.841%   $233.9503   $233.95   $233.95   $234.00  
  Purchase #2 $17.54   13.598%   $19.9251   $19.93   $19.95   $19.90  
  Purchase #3 $248.29   8.335%   $268.985   $268.99   $269.00   $269.00  
  Purchase #4 $181.26   13.709%   $206.1089   $206.11   $206.10   $206.10  
  Purchase #5 $73.81   8.831%   $80.3282   $80.33   $80.35   $80.30  
  Purchase #6 $234.97   5.578%   $248.0766   $248.08   $248.10   $248.10  
  Purchase #7 $54.72   10.351%   $60.3841   $60.38   $60.40   $60.40  
  7 purchase totals = $1,027.53       $1,117.7582   $1,117.77   $1,117.85   $1,117.80