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 $58.89   4.853%   $61.7479   $61.75   $61.75   $61.70  
  Purchase #2 $82.67   3.587%   $85.6354   $85.64   $85.65   $85.60  
  Purchase #3 $15.95   3.420%   $16.4955   $16.50   $16.50   $16.50  
  Purchase #4 $55.80   5.855%   $59.0671   $59.07   $59.05   $59.10  
  Purchase #5 $54.70   7.272%   $58.6778   $58.68   $58.70   $58.70  
  Purchase #6 $42.69   12.264%   $47.9255   $47.93   $47.95   $47.90  
  Purchase #7 $134.59   11.770%   $150.4312   $150.43   $150.45   $150.40  
  7 purchase totals = $445.29       $479.9804   $480.00   $480.05   $479.90