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 $201.62   12.569%   $226.9616   $226.96   $226.95   $227.00  
  Purchase #2 $28.74   11.575%   $32.0667   $32.07   $32.05   $32.10  
  Purchase #3 $131.70   12.560%   $148.2415   $148.24   $148.25   $148.20  
  Purchase #4 $179.87   10.617%   $198.9668   $198.97   $198.95   $199.00  
  Purchase #5 $56.29   9.328%   $61.5407   $61.54   $61.55   $61.50  
  Purchase #6 $194.68   5.746%   $205.8663   $205.87   $205.85   $205.90  
  Purchase #7 $122.28   3.563%   $126.6368   $126.64   $126.65   $126.60  
  7 purchase totals = $915.18       $1,000.2804   $1,000.29   $1,000.25   $1,000.30