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 $97.73   8.678%   $106.211   $106.21   $106.20   $106.20  
  Purchase #2 $198.47   6.596%   $211.5611   $211.56   $211.55   $211.60  
  Purchase #3 $241.51   6.358%   $256.8652   $256.87   $256.85   $256.90  
  Purchase #4 $29.38   9.823%   $32.266   $32.27   $32.25   $32.30  
  Purchase #5 $71.39   7.728%   $76.907   $76.91   $76.90   $76.90  
  Purchase #6 $96.67   11.520%   $107.8064   $107.81   $107.80   $107.80  
  Purchase #7 $234.33   9.581%   $256.7812   $256.78   $256.80   $256.80  
  7 purchase totals = $969.48       $1,048.3979   $1,048.41   $1,048.35   $1,048.50