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 $58.66   4.407%   $61.2451   $61.25   $61.25   $61.20  
  Purchase #2 $111.63   10.830%   $123.7195   $123.72   $123.70   $123.70  
  Purchase #3 $164.56   8.309%   $178.2333   $178.23   $178.25   $178.20  
  Purchase #4 $247.44   8.444%   $268.3338   $268.33   $268.35   $268.30  
  Purchase #5 $148.90   11.715%   $166.3436   $166.34   $166.35   $166.30  
  Purchase #6 $168.98   8.481%   $183.3112   $183.31   $183.30   $183.30  
  Purchase #7 $43.67   9.514%   $47.8248   $47.82   $47.80   $47.80  
  7 purchase totals = $943.84       $1,029.0113   $1,029.00   $1,029.00   $1,028.80