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 $230.72   7.862%   $248.8592   $248.86   $248.85   $248.90  
  Purchase #2 $147.61   12.155%   $165.552   $165.55   $165.55   $165.60  
  Purchase #3 $50.40   11.156%   $56.0226   $56.02   $56.00   $56.00  
  Purchase #4 $159.35   10.394%   $175.9128   $175.91   $175.90   $175.90  
  Purchase #5 $165.37   10.440%   $182.6346   $182.63   $182.65   $182.60  
  Purchase #6 $175.97   10.824%   $195.017   $195.02   $195.00   $195.00  
  Purchase #7 $151.52   5.342%   $159.6142   $159.61   $159.60   $159.60  
  7 purchase totals = $1,080.94       $1,183.6124   $1,183.60   $1,183.55   $1,183.60