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 $194.70   6.250%   $206.8688   $206.87   $206.85   $206.90  
  Purchase #2 $183.88   9.437%   $201.2328   $201.23   $201.25   $201.20  
  Purchase #3 $124.46   5.838%   $131.726   $131.73   $131.75   $131.70  
  Purchase #4 $177.86   6.858%   $190.0576   $190.06   $190.05   $190.10  
  Purchase #5 $86.51   11.348%   $96.3272   $96.33   $96.35   $96.30  
  Purchase #6 $175.74   6.592%   $187.3248   $187.32   $187.30   $187.30  
  Purchase #7 $219.87   9.466%   $240.6829   $240.68   $240.70   $240.70  
  7 purchase totals = $1,163.02       $1,254.2201   $1,254.22   $1,254.25   $1,254.20