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 $63.63   3.418%   $65.8049   $65.80   $65.80   $65.80  
  Purchase #2 $126.27   6.383%   $134.3298   $134.33   $134.35   $134.30  
  Purchase #3 $234.91   8.610%   $255.1358   $255.14   $255.15   $255.10  
  Purchase #4 $221.44   11.660%   $247.2599   $247.26   $247.25   $247.30  
  Purchase #5 $193.63   9.276%   $211.5911   $211.59   $211.60   $211.60  
  Purchase #6 $218.58   9.287%   $238.8795   $238.88   $238.90   $238.90  
  Purchase #7 $225.79   11.280%   $251.2591   $251.26   $251.25   $251.30  
  7 purchase totals = $1,284.25       $1,404.2601   $1,404.26   $1,404.30   $1,404.30