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 $97.37   9.102%   $106.2326   $106.23   $106.25   $106.20  
  Purchase #2 $182.88   4.786%   $191.6326   $191.63   $191.65   $191.60  
  Purchase #3 $10.50   11.649%   $11.7231   $11.72   $11.70   $11.70  
  Purchase #4 $18.96   3.616%   $19.6456   $19.65   $19.65   $19.60  
  Purchase #5 $69.93   5.808%   $73.9915   $73.99   $74.00   $74.00  
  Purchase #6 $223.62   13.760%   $254.3901   $254.39   $254.40   $254.40  
  Purchase #7 $121.40   11.141%   $134.9252   $134.93   $134.95   $134.90  
  7 purchase totals = $724.66       $792.5407   $792.54   $792.60   $792.40