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 $24.64   5.758%   $26.0588   $26.06   $26.05   $26.10  
  Purchase #2 $201.36   6.479%   $214.4061   $214.41   $214.40   $214.40  
  Purchase #3 $65.40   5.652%   $69.0964   $69.10   $69.10   $69.10  
  Purchase #4 $31.77   3.388%   $32.8464   $32.85   $32.85   $32.80  
  Purchase #5 $29.51   5.299%   $31.0737   $31.07   $31.05   $31.10  
  Purchase #6 $83.57   9.272%   $91.3186   $91.32   $91.30   $91.30  
  Purchase #7 $56.93   6.816%   $60.8103   $60.81   $60.80   $60.80  
  7 purchase totals = $493.18       $525.6103   $525.62   $525.55   $525.60