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 $29.41   13.705%   $33.4406   $33.44   $33.45   $33.40  
  Purchase #2 $219.92   11.844%   $245.9673   $245.97   $245.95   $246.00  
  Purchase #3 $233.92   10.626%   $258.7763   $258.78   $258.80   $258.80  
  Purchase #4 $106.81   7.586%   $114.9126   $114.91   $114.90   $114.90  
  Purchase #5 $42.84   8.500%   $46.4814   $46.48   $46.50   $46.50  
  Purchase #6 $136.86   4.759%   $143.3732   $143.37   $143.35   $143.40  
  Purchase #7 $75.92   10.702%   $84.045   $84.05   $84.05   $84.00  
  7 purchase totals = $845.68       $926.9964   $927.00   $927.00   $927.00