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 $67.41   12.481%   $75.8234   $75.82   $75.80   $75.80  
  Purchase #2 $242.46   9.290%   $264.9845   $264.98   $265.00   $265.00  
  Purchase #3 $135.76   11.446%   $151.2991   $151.30   $151.30   $151.30  
  Purchase #4 $45.44   11.229%   $50.5425   $50.54   $50.55   $50.50  
  Purchase #5 $145.99   7.357%   $156.7305   $156.73   $156.75   $156.70  
  Purchase #6 $171.30   9.335%   $187.2909   $187.29   $187.30   $187.30  
  Purchase #7 $72.32   6.126%   $76.7503   $76.75   $76.75   $76.80  
  7 purchase totals = $880.68       $963.4212   $963.41   $963.45   $963.40