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 $112.32   11.789%   $125.5614   $125.56   $125.55   $125.60  
  Purchase #2 $58.51   7.681%   $63.0042   $63.00   $63.00   $63.00  
  Purchase #3 $209.50   6.368%   $222.841   $222.84   $222.85   $222.80  
  Purchase #4 $57.39   5.107%   $60.3209   $60.32   $60.30   $60.30  
  Purchase #5 $164.58   12.325%   $184.8645   $184.86   $184.85   $184.90  
  Purchase #6 $104.55   10.189%   $115.2026   $115.20   $115.20   $115.20  
  Purchase #7 $194.65   9.328%   $212.807   $212.81   $212.80   $212.80  
  7 purchase totals = $901.50       $984.6016   $984.59   $984.55   $984.60