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 $31.93   5.204%   $33.5916   $33.59   $33.60   $33.60  
  Purchase #2 $199.86   3.215%   $206.2855   $206.29   $206.30   $206.30  
  Purchase #3 $64.29   5.177%   $67.6183   $67.62   $67.60   $67.60  
  Purchase #4 $124.60   12.540%   $140.2248   $140.22   $140.20   $140.20  
  Purchase #5 $48.67   5.779%   $51.4826   $51.48   $51.50   $51.50  
  Purchase #6 $186.25   7.177%   $199.6172   $199.62   $199.60   $199.60  
  Purchase #7 $64.96   5.357%   $68.4399   $68.44   $68.45   $68.40  
  7 purchase totals = $720.56       $767.2599   $767.26   $767.25   $767.20