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 $22.99   10.124%   $25.3175   $25.32   $25.30   $25.30  
  Purchase #2 $32.84   9.579%   $35.9857   $35.99   $36.00   $36.00  
  Purchase #3 $162.34   4.193%   $169.1469   $169.15   $169.15   $169.10  
  Purchase #4 $208.86   6.174%   $221.755   $221.76   $221.75   $221.80  
  Purchase #5 $149.36   12.160%   $167.5222   $167.52   $167.50   $167.50  
  Purchase #6 $206.25   7.872%   $222.486   $222.49   $222.50   $222.50  
  Purchase #7 $170.91   11.751%   $190.9936   $190.99   $191.00   $191.00  
  7 purchase totals = $953.55       $1,033.2069   $1,033.22   $1,033.20   $1,033.20