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 $92.27   4.671%   $96.5799   $96.58   $96.60   $96.60  
  Purchase #2 $149.94   8.167%   $162.1856   $162.19   $162.20   $162.20  
  Purchase #3 $69.81   3.864%   $72.5075   $72.51   $72.50   $72.50  
  Purchase #4 $206.78   11.295%   $230.1358   $230.14   $230.15   $230.10  
  Purchase #5 $132.78   4.328%   $138.5267   $138.53   $138.55   $138.50  
  Purchase #6 $149.57   3.234%   $154.4071   $154.41   $154.40   $154.40  
  Purchase #7 $47.70   12.782%   $53.797   $53.80   $53.80   $53.80  
  7 purchase totals = $848.85       $908.1396   $908.16   $908.20   $908.10