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 $184.25   13.306%   $208.7663   $208.77   $208.75   $208.80  
  Purchase #2 $222.96   13.626%   $253.3405   $253.34   $253.35   $253.30  
  Purchase #3 $144.52   8.787%   $157.219   $157.22   $157.20   $157.20  
  Purchase #4 $56.55   5.742%   $59.7971   $59.80   $59.80   $59.80  
  Purchase #5 $169.48   4.360%   $176.8693   $176.87   $176.85   $176.90  
  Purchase #6 $80.37   10.274%   $88.6272   $88.63   $88.65   $88.60  
  Purchase #7 $180.74   6.201%   $191.9477   $191.95   $191.95   $191.90  
  7 purchase totals = $1,038.87       $1,136.5671   $1,136.58   $1,136.55   $1,136.50