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 $33.54   3.423%   $34.6881   $34.69   $34.70   $34.70  
  Purchase #2 $150.59   11.410%   $167.7723   $167.77   $167.75   $167.80  
  Purchase #3 $176.36   5.505%   $186.0686   $186.07   $186.05   $186.10  
  Purchase #4 $220.57   5.158%   $231.947   $231.95   $231.95   $231.90  
  Purchase #5 $32.80   6.327%   $34.8753   $34.88   $34.90   $34.90  
  Purchase #6 $187.31   13.677%   $212.9284   $212.93   $212.95   $212.90  
  Purchase #7 $76.46   11.154%   $84.9883   $84.99   $85.00   $85.00  
  7 purchase totals = $877.63       $953.2680   $953.28   $953.30   $953.30