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 $100.33   7.104%   $107.4574   $107.46   $107.45   $107.50  
  Purchase #2 $21.37   3.620%   $22.1436   $22.14   $22.15   $22.10  
  Purchase #3 $31.41   6.537%   $33.4633   $33.46   $33.45   $33.50  
  Purchase #4 $39.87   10.121%   $43.9052   $43.91   $43.90   $43.90  
  Purchase #5 $226.61   9.837%   $248.9016   $248.90   $248.90   $248.90  
  Purchase #6 $75.55   10.792%   $83.7034   $83.70   $83.70   $83.70  
  Purchase #7 $29.44   5.842%   $31.1599   $31.16   $31.15   $31.20  
  7 purchase totals = $524.58       $570.7344   $570.73   $570.70   $570.80