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 $57.99   7.425%   $62.2958   $62.30   $62.30   $62.30  
  Purchase #2 $111.32   5.584%   $117.5361   $117.54   $117.55   $117.50  
  Purchase #3 $166.94   12.567%   $187.9193   $187.92   $187.90   $187.90  
  Purchase #4 $249.96   6.688%   $266.6773   $266.68   $266.70   $266.70  
  Purchase #5 $128.97   10.285%   $142.2346   $142.23   $142.25   $142.20  
  Purchase #6 $36.90   11.704%   $41.2188   $41.22   $41.20   $41.20  
  Purchase #7 $183.28   12.231%   $205.697   $205.70   $205.70   $205.70  
  7 purchase totals = $935.36       $1,023.5789   $1,023.59   $1,023.60   $1,023.50