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 $58.87   7.156%   $63.0827   $63.08   $63.10   $63.10  
  Purchase #2 $182.28   11.795%   $203.7799   $203.78   $203.80   $203.80  
  Purchase #3 $201.72   3.575%   $208.9315   $208.93   $208.95   $208.90  
  Purchase #4 $76.91   11.500%   $85.7547   $85.75   $85.75   $85.80  
  Purchase #5 $33.40   11.434%   $37.219   $37.22   $37.20   $37.20  
  Purchase #6 $117.75   5.371%   $124.0744   $124.07   $124.05   $124.10  
  Purchase #7 $243.49   3.521%   $252.0633   $252.06   $252.05   $252.10  
  7 purchase totals = $914.42       $974.9055   $974.89   $974.90   $975.00