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 $71.82   6.184%   $76.2613   $76.26   $76.25   $76.30  
  Purchase #2 $196.37   5.331%   $206.8385   $206.84   $206.85   $206.80  
  Purchase #3 $176.37   12.403%   $198.2452   $198.25   $198.25   $198.20  
  Purchase #4 $110.38   8.507%   $119.77   $119.77   $119.75   $119.80  
  Purchase #5 $158.64   5.314%   $167.0701   $167.07   $167.05   $167.10  
  Purchase #6 $64.85   6.210%   $68.8772   $68.88   $68.90   $68.90  
  Purchase #7 $239.42   5.856%   $253.4404   $253.44   $253.45   $253.40  
  7 purchase totals = $1,017.85       $1,090.5027   $1,090.51   $1,090.50   $1,090.50