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 $52.38   13.239%   $59.3146   $59.31   $59.30   $59.30  
  Purchase #2 $182.80   3.377%   $188.9732   $188.97   $188.95   $189.00  
  Purchase #3 $214.31   13.412%   $243.0533   $243.05   $243.05   $243.10  
  Purchase #4 $160.87   11.831%   $179.9025   $179.90   $179.90   $179.90  
  Purchase #5 $178.43   8.183%   $193.0309   $193.03   $193.05   $193.00  
  Purchase #6 $162.75   12.110%   $182.459   $182.46   $182.45   $182.50  
  Purchase #7 $23.55   5.391%   $24.8196   $24.82   $24.80   $24.80  
  7 purchase totals = $975.09       $1,071.5531   $1,071.54   $1,071.50   $1,071.60