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 $114.89   4.301%   $119.8314   $119.83   $119.85   $119.80  
  Purchase #2 $165.52   10.135%   $182.2955   $182.30   $182.30   $182.30  
  Purchase #3 $222.65   11.830%   $248.9895   $248.99   $249.00   $249.00  
  Purchase #4 $51.31   11.191%   $57.0521   $57.05   $57.05   $57.10  
  Purchase #5 $201.89   5.115%   $212.2167   $212.22   $212.20   $212.20  
  Purchase #6 $69.48   10.511%   $76.783   $76.78   $76.80   $76.80  
  Purchase #7 $113.59   11.625%   $126.7948   $126.79   $126.80   $126.80  
  7 purchase totals = $939.33       $1,023.9630   $1,023.96   $1,024.00   $1,024.00