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 $40.68   9.556%   $44.5674   $44.57   $44.55   $44.60  
  Purchase #2 $209.99   12.818%   $236.9065   $236.91   $236.90   $236.90  
  Purchase #3 $228.52   5.671%   $241.4794   $241.48   $241.50   $241.50  
  Purchase #4 $21.60   11.204%   $24.0201   $24.02   $24.00   $24.00  
  Purchase #5 $52.92   10.273%   $58.3565   $58.36   $58.35   $58.40  
  Purchase #6 $250.83   6.110%   $266.1557   $266.16   $266.15   $266.20  
  Purchase #7 $52.59   9.446%   $57.5577   $57.56   $57.55   $57.60  
  7 purchase totals = $857.13       $929.0433   $929.06   $929.00   $929.20