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 $6.91   11.136%   $7.6795   $7.68   $7.70   $7.70  
  Purchase #2 $106.27   7.568%   $114.3125   $114.31   $114.30   $114.30  
  Purchase #3 $236.33   6.631%   $252.001   $252.00   $252.00   $252.00  
  Purchase #4 $102.94   11.422%   $114.6978   $114.70   $114.70   $114.70  
  Purchase #5 $68.84   5.337%   $72.514   $72.51   $72.50   $72.50  
  Purchase #6 $227.95   5.725%   $241.0001   $241.00   $241.00   $241.00  
  Purchase #7 $26.97   10.568%   $29.8202   $29.82   $29.80   $29.80  
  7 purchase totals = $776.21       $832.0251   $832.02   $832.00   $832.00