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 $23.58   12.867%   $26.614   $26.61   $26.60   $26.60  
  Purchase #2 $103.68   4.380%   $108.2212   $108.22   $108.20   $108.20  
  Purchase #3 $250.87   12.227%   $281.5439   $281.54   $281.55   $281.50  
  Purchase #4 $173.44   10.413%   $191.5003   $191.50   $191.50   $191.50  
  Purchase #5 $162.89   13.385%   $184.6928   $184.69   $184.70   $184.70  
  Purchase #6 $137.76   12.675%   $155.2211   $155.22   $155.20   $155.20  
  Purchase #7 $121.46   13.868%   $138.3041   $138.30   $138.30   $138.30  
  7 purchase totals = $973.68       $1,086.0974   $1,086.08   $1,086.05   $1,086.00