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 $57.86   8.431%   $62.7382   $62.74   $62.75   $62.70  
  Purchase #2 $122.86   8.686%   $133.5316   $133.53   $133.55   $133.50  
  Purchase #3 $14.86   12.567%   $16.7275   $16.73   $16.75   $16.70  
  Purchase #4 $188.89   8.623%   $205.178   $205.18   $205.20   $205.20  
  Purchase #5 $241.30   4.469%   $252.0837   $252.08   $252.10   $252.10  
  Purchase #6 $100.41   13.725%   $114.1913   $114.19   $114.20   $114.20  
  Purchase #7 $71.58   12.182%   $80.2999   $80.30   $80.30   $80.30  
  7 purchase totals = $797.76       $864.7502   $864.75   $864.85   $864.70