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 $49.42   8.411%   $53.5767   $53.58   $53.60   $53.60  
  Purchase #2 $85.81   6.342%   $91.2521   $91.25   $91.25   $91.30  
  Purchase #3 $121.25   13.479%   $137.5933   $137.59   $137.60   $137.60  
  Purchase #4 $220.77   7.263%   $236.8045   $236.80   $236.80   $236.80  
  Purchase #5 $15.25   6.457%   $16.2347   $16.23   $16.25   $16.20  
  Purchase #6 $79.61   8.147%   $86.0958   $86.10   $86.10   $86.10  
  Purchase #7 $114.29   10.245%   $125.999   $126.00   $126.00   $126.00  
  7 purchase totals = $686.40       $747.5561   $747.55   $747.60   $747.60