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 $29.73   9.658%   $32.6013   $32.60   $32.60   $32.60  
  Purchase #2 $94.83   10.862%   $105.1304   $105.13   $105.15   $105.10  
  Purchase #3 $79.99   5.860%   $84.6774   $84.68   $84.70   $84.70  
  Purchase #4 $23.55   12.253%   $26.4356   $26.44   $26.45   $26.40  
  Purchase #5 $96.29   3.701%   $99.8537   $99.85   $99.85   $99.90  
  Purchase #6 $229.48   10.766%   $254.1858   $254.19   $254.20   $254.20  
  Purchase #7 $124.74   13.835%   $141.9978   $142.00   $142.00   $142.00  
  7 purchase totals = $678.61       $744.8820   $744.89   $744.95   $744.90