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 $86.41   13.659%   $98.2127   $98.21   $98.20   $98.20  
  Purchase #2 $207.97   9.512%   $227.7521   $227.75   $227.75   $227.80  
  Purchase #3 $175.69   4.608%   $183.7858   $183.79   $183.80   $183.80  
  Purchase #4 $156.52   3.697%   $162.3065   $162.31   $162.30   $162.30  
  Purchase #5 $238.87   3.439%   $247.0847   $247.08   $247.10   $247.10  
  Purchase #6 $134.62   13.512%   $152.8099   $152.81   $152.80   $152.80  
  Purchase #7 $236.63   13.674%   $268.9868   $268.99   $269.00   $269.00  
  7 purchase totals = $1,236.71       $1,340.9385   $1,340.94   $1,340.95   $1,341.00