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 $234.95   11.575%   $262.1455   $262.15   $262.15   $262.10  
  Purchase #2 $198.74   9.874%   $218.3636   $218.36   $218.35   $218.40  
  Purchase #3 $57.58   6.222%   $61.1626   $61.16   $61.15   $61.20  
  Purchase #4 $159.85   6.307%   $169.9317   $169.93   $169.95   $169.90  
  Purchase #5 $241.98   9.290%   $264.4599   $264.46   $264.45   $264.50  
  Purchase #6 $175.41   7.189%   $188.0202   $188.02   $188.00   $188.00  
  Purchase #7 $11.36   4.391%   $11.8588   $11.86   $11.85   $11.90  
  7 purchase totals = $1,079.87       $1,175.9423   $1,175.94   $1,175.90   $1,176.00