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 $217.93   11.458%   $242.9004   $242.90   $242.90   $242.90  
  Purchase #2 $140.92   5.436%   $148.5804   $148.58   $148.60   $148.60  
  Purchase #3 $53.35   6.662%   $56.9042   $56.90   $56.90   $56.90  
  Purchase #4 $195.57   12.463%   $219.9439   $219.94   $219.95   $219.90  
  Purchase #5 $186.77   10.435%   $206.2594   $206.26   $206.25   $206.30  
  Purchase #6 $226.41   12.223%   $254.0841   $254.08   $254.10   $254.10  
  Purchase #7 $145.97   11.656%   $162.9843   $162.98   $163.00   $163.00  
  7 purchase totals = $1,166.92       $1,291.6567   $1,291.64   $1,291.70   $1,291.70