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 $7.76   12.774%   $8.7513   $8.75   $8.75   $8.80  
  Purchase #2 $118.51   4.581%   $123.9389   $123.94   $123.95   $123.90  
  Purchase #3 $191.29   5.605%   $202.0118   $202.01   $202.00   $202.00  
  Purchase #4 $234.70   5.243%   $247.0053   $247.01   $247.00   $247.00  
  Purchase #5 $22.81   8.263%   $24.6948   $24.69   $24.70   $24.70  
  Purchase #6 $212.93   11.539%   $237.5   $237.50   $237.50   $237.50  
  Purchase #7 $194.58   10.805%   $215.6044   $215.60   $215.60   $215.60  
  7 purchase totals = $982.58       $1,059.5065   $1,059.50   $1,059.50   $1,059.50