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 $183.95   5.840%   $194.6927   $194.69   $194.70   $194.70  
  Purchase #2 $17.56   6.841%   $18.7613   $18.76   $18.75   $18.80  
  Purchase #3 $179.52   4.139%   $186.9503   $186.95   $186.95   $187.00  
  Purchase #4 $131.55   11.563%   $146.7611   $146.76   $146.75   $146.80  
  Purchase #5 $208.38   9.334%   $227.8302   $227.83   $227.85   $227.80  
  Purchase #6 $124.83   11.818%   $139.5824   $139.58   $139.60   $139.60  
  Purchase #7 $20.32   9.852%   $22.3219   $22.32   $22.30   $22.30  
  7 purchase totals = $866.11       $936.8999   $936.89   $936.90   $937.00