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 $115.58   3.469%   $119.5895   $119.59   $119.60   $119.60  
  Purchase #2 $162.38   8.395%   $176.0118   $176.01   $176.00   $176.00  
  Purchase #3 $15.99   4.513%   $16.7116   $16.71   $16.70   $16.70  
  Purchase #4 $231.54   11.640%   $258.4913   $258.49   $258.50   $258.50  
  Purchase #5 $79.76   3.459%   $82.5189   $82.52   $82.50   $82.50  
  Purchase #6 $202.69   4.518%   $211.8475   $211.85   $211.85   $211.80  
  Purchase #7 $52.93   11.203%   $58.8597   $58.86   $58.85   $58.90  
  7 purchase totals = $860.87       $924.0303   $924.03   $924.00   $924.00