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 $162.59   13.566%   $184.647   $184.65   $184.65   $184.60  
  Purchase #2 $76.55   7.440%   $82.2453   $82.25   $82.25   $82.20  
  Purchase #3 $165.41   7.765%   $178.2541   $178.25   $178.25   $178.30  
  Purchase #4 $83.98   3.291%   $86.7438   $86.74   $86.75   $86.70  
  Purchase #5 $212.93   3.191%   $219.7246   $219.72   $219.70   $219.70  
  Purchase #6 $143.84   13.805%   $163.6971   $163.70   $163.70   $163.70  
  Purchase #7 $109.42   3.707%   $113.4762   $113.48   $113.50   $113.50  
  7 purchase totals = $954.72       $1,028.7881   $1,028.79   $1,028.80   $1,028.70