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 $184.58   13.587%   $209.6589   $209.66   $209.65   $209.70  
  Purchase #2 $47.98   9.215%   $52.4014   $52.40   $52.40   $52.40  
  Purchase #3 $248.67   6.190%   $264.0627   $264.06   $264.05   $264.10  
  Purchase #4 $58.99   13.614%   $67.0209   $67.02   $67.00   $67.00  
  Purchase #5 $193.91   8.447%   $210.2896   $210.29   $210.30   $210.30  
  Purchase #6 $236.56   13.558%   $268.6328   $268.63   $268.65   $268.60  
  Purchase #7 $150.26   13.769%   $170.9493   $170.95   $170.95   $170.90  
  7 purchase totals = $1,120.95       $1,243.0156   $1,243.01   $1,243.00   $1,243.00