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 $83.68   3.147%   $86.3134   $86.31   $86.30   $86.30  
  Purchase #2 $247.28   12.133%   $277.2825   $277.28   $277.30   $277.30  
  Purchase #3 $82.74   4.788%   $86.7016   $86.70   $86.70   $86.70  
  Purchase #4 $65.95   13.866%   $75.0946   $75.09   $75.10   $75.10  
  Purchase #5 $42.27   11.191%   $47.0004   $47.00   $47.00   $47.00  
  Purchase #6 $214.98   13.808%   $244.6644   $244.66   $244.65   $244.70  
  Purchase #7 $167.33   9.375%   $183.0172   $183.02   $183.00   $183.00  
  7 purchase totals = $904.23       $1,000.0741   $1,000.06   $1,000.05   $1,000.10