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 $232.76   13.432%   $264.0243   $264.02   $264.00   $264.00  
  Purchase #2 $31.57   8.330%   $34.1998   $34.20   $34.20   $34.20  
  Purchase #3 $196.32   9.266%   $214.511   $214.51   $214.50   $214.50  
  Purchase #4 $67.66   11.387%   $75.3644   $75.36   $75.35   $75.40  
  Purchase #5 $215.91   10.769%   $239.1613   $239.16   $239.15   $239.20  
  Purchase #6 $114.52   10.469%   $126.5091   $126.51   $126.50   $126.50  
  Purchase #7 $121.62   6.475%   $129.4949   $129.49   $129.50   $129.50  
  7 purchase totals = $980.36       $1,083.2648   $1,083.25   $1,083.20   $1,083.30