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 $101.45   6.294%   $107.8353   $107.84   $107.85   $107.80  
  Purchase #2 $115.48   4.837%   $121.0658   $121.07   $121.05   $121.10  
  Purchase #3 $138.88   8.580%   $150.7959   $150.80   $150.80   $150.80  
  Purchase #4 $105.64   8.431%   $114.5465   $114.55   $114.55   $114.50  
  Purchase #5 $27.53   8.506%   $29.8717   $29.87   $29.85   $29.90  
  Purchase #6 $33.77   12.228%   $37.8994   $37.90   $37.90   $37.90  
  Purchase #7 $144.68   10.705%   $160.168   $160.17   $160.15   $160.20  
  7 purchase totals = $667.43       $722.1826   $722.20   $722.15   $722.20