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 $22.63   6.543%   $24.1107   $24.11   $24.10   $24.10  
  Purchase #2 $183.28   7.648%   $197.2973   $197.30   $197.30   $197.30  
  Purchase #3 $233.39   5.871%   $247.0923   $247.09   $247.10   $247.10  
  Purchase #4 $242.63   11.277%   $269.9914   $269.99   $270.00   $270.00  
  Purchase #5 $113.79   11.751%   $127.1615   $127.16   $127.15   $127.20  
  Purchase #6 $101.70   5.817%   $107.6159   $107.62   $107.60   $107.60  
  Purchase #7 $230.85   5.372%   $243.2513   $243.25   $243.25   $243.30  
  7 purchase totals = $1,128.27       $1,216.5204   $1,216.52   $1,216.50   $1,216.60