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 $67.77   3.273%   $69.9881   $69.99   $70.00   $70.00  
  Purchase #2 $236.41   6.279%   $251.2542   $251.25   $251.25   $251.30  
  Purchase #3 $239.41   6.263%   $254.4042   $254.40   $254.40   $254.40  
  Purchase #4 $25.25   11.843%   $28.2404   $28.24   $28.25   $28.20  
  Purchase #5 $182.81   8.867%   $199.0198   $199.02   $199.00   $199.00  
  Purchase #6 $6.99   11.564%   $7.7983   $7.80   $7.80   $7.80  
  Purchase #7 $104.74   8.403%   $113.5413   $113.54   $113.55   $113.50  
  7 purchase totals = $863.38       $924.2463   $924.24   $924.25   $924.20