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 $84.50   8.747%   $91.8912   $91.89   $91.90   $91.90  
  Purchase #2 $176.53   13.274%   $199.9626   $199.96   $199.95   $200.00  
  Purchase #3 $234.37   13.567%   $266.167   $266.17   $266.15   $266.20  
  Purchase #4 $23.43   11.759%   $26.1851   $26.19   $26.20   $26.20  
  Purchase #5 $145.68   12.790%   $164.3125   $164.31   $164.30   $164.30  
  Purchase #6 $226.72   9.428%   $248.0952   $248.10   $248.10   $248.10  
  Purchase #7 $14.46   13.729%   $16.4452   $16.45   $16.45   $16.40  
  7 purchase totals = $905.69       $1,013.0588   $1,013.07   $1,013.05   $1,013.10