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 $236.64   11.277%   $263.3259   $263.33   $263.35   $263.30  
  Purchase #2 $196.93   4.310%   $205.4177   $205.42   $205.40   $205.40  
  Purchase #3 $93.77   4.182%   $97.6915   $97.69   $97.70   $97.70  
  Purchase #4 $237.96   13.382%   $269.8038   $269.80   $269.80   $269.80  
  Purchase #5 $78.71   3.643%   $81.5774   $81.58   $81.60   $81.60  
  Purchase #6 $48.94   6.176%   $51.9625   $51.96   $51.95   $52.00  
  Purchase #7 $191.50   12.443%   $215.3283   $215.33   $215.35   $215.30  
  7 purchase totals = $1,084.45       $1,185.1071   $1,185.11   $1,185.15   $1,185.10