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 $245.77   3.494%   $254.3572   $254.36   $254.35   $254.40  
  Purchase #2 $33.58   12.359%   $37.7302   $37.73   $37.75   $37.70  
  Purchase #3 $22.36   9.458%   $24.4748   $24.47   $24.45   $24.50  
  Purchase #4 $102.99   10.817%   $114.1304   $114.13   $114.15   $114.10  
  Purchase #5 $244.63   8.336%   $265.0224   $265.02   $265.00   $265.00  
  Purchase #6 $77.99   11.777%   $87.1749   $87.17   $87.15   $87.20  
  Purchase #7 $15.56   3.708%   $16.137   $16.14   $16.15   $16.10  
  7 purchase totals = $742.88       $799.0269   $799.02   $799.00   $799.00