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 $86.59   7.193%   $92.8184   $92.82   $92.80   $92.80  
  Purchase #2 $53.98   4.140%   $56.2148   $56.21   $56.20   $56.20  
  Purchase #3 $239.86   7.773%   $258.5043   $258.50   $258.50   $258.50  
  Purchase #4 $206.75   11.526%   $230.58   $230.58   $230.60   $230.60  
  Purchase #5 $79.76   3.514%   $82.5628   $82.56   $82.55   $82.60  
  Purchase #6 $106.75   3.649%   $110.6453   $110.65   $110.65   $110.60  
  Purchase #7 $149.71   10.385%   $165.2574   $165.26   $165.25   $165.30  
  7 purchase totals = $923.40       $996.5830   $996.58   $996.55   $996.60