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 $6.77   5.200%   $7.122   $7.12   $7.10   $7.10  
  Purchase #2 $173.36   8.316%   $187.7766   $187.78   $187.80   $187.80  
  Purchase #3 $196.29   9.838%   $215.601   $215.60   $215.60   $215.60  
  Purchase #4 $167.52   4.382%   $174.8607   $174.86   $174.85   $174.90  
  Purchase #5 $135.56   5.453%   $142.9521   $142.95   $142.95   $143.00  
  Purchase #6 $107.30   4.370%   $111.989   $111.99   $112.00   $112.00  
  Purchase #7 $239.58   3.616%   $248.2432   $248.24   $248.25   $248.20  
  7 purchase totals = $1,026.38       $1,088.5446   $1,088.54   $1,088.55   $1,088.60