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 $206.29   4.214%   $214.9831   $214.98   $215.00   $215.00  
  Purchase #2 $237.62   12.695%   $267.7859   $267.79   $267.80   $267.80  
  Purchase #3 $180.88   7.547%   $194.531   $194.53   $194.55   $194.50  
  Purchase #4 $184.49   8.149%   $199.5241   $199.52   $199.50   $199.50  
  Purchase #5 $172.90   13.187%   $195.7003   $195.70   $195.70   $195.70  
  Purchase #6 $159.95   8.499%   $173.5442   $173.54   $173.55   $173.50  
  Purchase #7 $32.62   8.864%   $35.5114   $35.51   $35.50   $35.50  
  7 purchase totals = $1,174.75       $1,281.5800   $1,281.57   $1,281.60   $1,281.50