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 $24.48   6.218%   $26.0022   $26.00   $26.00   $26.00  
  Purchase #2 $117.96   3.245%   $121.7878   $121.79   $121.80   $121.80  
  Purchase #3 $114.25   8.365%   $123.807   $123.81   $123.80   $123.80  
  Purchase #4 $168.59   4.222%   $175.7079   $175.71   $175.70   $175.70  
  Purchase #5 $136.84   11.634%   $152.76   $152.76   $152.75   $152.80  
  Purchase #6 $67.34   5.448%   $71.0087   $71.01   $71.00   $71.00  
  Purchase #7 $234.73   5.481%   $247.5956   $247.60   $247.60   $247.60  
  7 purchase totals = $864.19       $918.6692   $918.68   $918.65   $918.70