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 $23.55   8.728%   $25.6054   $25.61   $25.60   $25.60  
  Purchase #2 $75.94   3.112%   $78.3033   $78.30   $78.30   $78.30  
  Purchase #3 $186.43   13.182%   $211.0052   $211.01   $211.00   $211.00  
  Purchase #4 $242.87   3.721%   $251.9072   $251.91   $251.90   $251.90  
  Purchase #5 $245.47   8.158%   $265.4954   $265.50   $265.50   $265.50  
  Purchase #6 $29.73   5.226%   $31.2837   $31.28   $31.30   $31.30  
  Purchase #7 $147.89   12.262%   $166.0243   $166.02   $166.00   $166.00  
  7 purchase totals = $951.88       $1,029.6245   $1,029.63   $1,029.60   $1,029.60