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 $96.51   8.525%   $104.7375   $104.74   $104.75   $104.70  
  Purchase #2 $57.47   6.272%   $61.0745   $61.07   $61.05   $61.10  
  Purchase #3 $246.79   7.859%   $266.1852   $266.19   $266.20   $266.20  
  Purchase #4 $143.94   13.607%   $163.5259   $163.53   $163.55   $163.50  
  Purchase #5 $185.28   5.368%   $195.2258   $195.23   $195.25   $195.20  
  Purchase #6 $236.37   13.286%   $267.7741   $267.77   $267.75   $267.80  
  Purchase #7 $19.95   3.715%   $20.6911   $20.69   $20.70   $20.70  
  7 purchase totals = $986.31       $1,079.2141   $1,079.22   $1,079.25   $1,079.20