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 $73.44   13.638%   $83.4557   $83.46   $83.45   $83.50  
  Purchase #2 $205.58   12.694%   $231.6763   $231.68   $231.70   $231.70  
  Purchase #3 $237.76   10.290%   $262.2255   $262.23   $262.25   $262.20  
  Purchase #4 $200.52   11.157%   $222.892   $222.89   $222.90   $222.90  
  Purchase #5 $192.69   6.678%   $205.5578   $205.56   $205.55   $205.60  
  Purchase #6 $11.49   11.738%   $12.8387   $12.84   $12.85   $12.80  
  Purchase #7 $14.61   13.717%   $16.6141   $16.61   $16.60   $16.60  
  7 purchase totals = $936.09       $1,035.2601   $1,035.27   $1,035.30   $1,035.30