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 $101.87   12.218%   $114.3165   $114.32   $114.30   $114.30  
  Purchase #2 $159.49   7.765%   $171.8744   $171.87   $171.85   $171.90  
  Purchase #3 $33.69   12.838%   $38.0151   $38.02   $38.00   $38.00  
  Purchase #4 $76.27   11.524%   $85.0594   $85.06   $85.05   $85.10  
  Purchase #5 $142.41   6.453%   $151.5997   $151.60   $151.60   $151.60  
  Purchase #6 $125.28   3.386%   $129.522   $129.52   $129.50   $129.50  
  Purchase #7 $106.99   10.346%   $118.0592   $118.06   $118.05   $118.10  
  7 purchase totals = $746.00       $808.4463   $808.45   $808.35   $808.50