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 $24.55   3.220%   $25.3405   $25.34   $25.35   $25.30  
  Purchase #2 $119.30   7.717%   $128.5064   $128.51   $128.50   $128.50  
  Purchase #3 $102.71   13.855%   $116.9405   $116.94   $116.95   $116.90  
  Purchase #4 $183.63   12.293%   $206.2036   $206.20   $206.20   $206.20  
  Purchase #5 $48.44   12.702%   $54.5928   $54.59   $54.60   $54.60  
  Purchase #6 $95.68   3.278%   $98.8164   $98.82   $98.80   $98.80  
  Purchase #7 $56.88   12.384%   $63.924   $63.92   $63.90   $63.90  
  7 purchase totals = $631.19       $694.3242   $694.32   $694.30   $694.20