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 $187.63   8.721%   $203.9932   $203.99   $204.00   $204.00  
  Purchase #2 $195.92   4.820%   $205.3633   $205.36   $205.35   $205.40  
  Purchase #3 $216.27   4.491%   $225.9827   $225.98   $226.00   $226.00  
  Purchase #4 $156.80   8.258%   $169.7485   $169.75   $169.75   $169.70  
  Purchase #5 $104.45   4.316%   $108.9581   $108.96   $108.95   $109.00  
  Purchase #6 $248.94   5.221%   $261.9372   $261.94   $261.95   $261.90  
  Purchase #7 $115.81   6.704%   $123.5739   $123.57   $123.55   $123.60  
  7 purchase totals = $1,225.82       $1,299.5569   $1,299.55   $1,299.55   $1,299.60