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 $59.76   3.333%   $61.7518   $61.75   $61.75   $61.80  
  Purchase #2 $30.90   3.654%   $32.0291   $32.03   $32.05   $32.00  
  Purchase #3 $208.99   5.627%   $220.7499   $220.75   $220.75   $220.70  
  Purchase #4 $6.41   6.715%   $6.8404   $6.84   $6.85   $6.80  
  Purchase #5 $53.29   6.282%   $56.6377   $56.64   $56.65   $56.60  
  Purchase #6 $48.56   6.736%   $51.831   $51.83   $51.85   $51.80  
  Purchase #7 $127.39   13.189%   $144.1915   $144.19   $144.20   $144.20  
  7 purchase totals = $535.30       $574.0314   $574.03   $574.10   $573.90