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 $151.61   8.790%   $164.9365   $164.94   $164.95   $164.90  
  Purchase #2 $140.89   12.102%   $157.9405   $157.94   $157.95   $157.90  
  Purchase #3 $240.52   11.810%   $268.9254   $268.93   $268.95   $268.90  
  Purchase #4 $96.37   11.705%   $107.6501   $107.65   $107.65   $107.70  
  Purchase #5 $214.77   12.181%   $240.9311   $240.93   $240.95   $240.90  
  Purchase #6 $215.43   7.626%   $231.8587   $231.86   $231.85   $231.90  
  Purchase #7 $134.60   11.211%   $149.69   $149.69   $149.70   $149.70  
  7 purchase totals = $1,194.19       $1,321.9323   $1,321.94   $1,322.00   $1,321.90