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 $86.94   8.372%   $94.2186   $94.22   $94.20   $94.20  
  Purchase #2 $148.57   8.434%   $161.1004   $161.10   $161.10   $161.10  
  Purchase #3 $60.67   10.658%   $67.1362   $67.14   $67.15   $67.10  
  Purchase #4 $144.33   10.737%   $159.8267   $159.83   $159.85   $159.80  
  Purchase #5 $237.54   8.531%   $257.8045   $257.80   $257.80   $257.80  
  Purchase #6 $67.31   8.861%   $73.2743   $73.27   $73.25   $73.30  
  Purchase #7 $109.34   4.541%   $114.3051   $114.31   $114.30   $114.30  
  7 purchase totals = $854.70       $927.6658   $927.67   $927.65   $927.60