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 $89.27   5.144%   $93.862   $93.86   $93.85   $93.90  
  Purchase #2 $168.47   5.558%   $177.8336   $177.83   $177.85   $177.80  
  Purchase #3 $123.79   10.150%   $136.3547   $136.35   $136.35   $136.40  
  Purchase #4 $67.73   7.298%   $72.6729   $72.67   $72.65   $72.70  
  Purchase #5 $68.75   11.388%   $76.5793   $76.58   $76.60   $76.60  
  Purchase #6 $106.86   6.708%   $114.0282   $114.03   $114.05   $114.00  
  Purchase #7 $232.53   6.481%   $247.6003   $247.60   $247.60   $247.60  
  7 purchase totals = $857.40       $918.9310   $918.92   $918.95   $919.00