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 $22.74   11.262%   $25.301   $25.30   $25.30   $25.30  
  Purchase #2 $60.79   12.193%   $68.2021   $68.20   $68.20   $68.20  
  Purchase #3 $125.83   13.757%   $143.1404   $143.14   $143.15   $143.10  
  Purchase #4 $188.55   5.299%   $198.5413   $198.54   $198.55   $198.50  
  Purchase #5 $61.46   12.395%   $69.078   $69.08   $69.10   $69.10  
  Purchase #6 $69.28   7.588%   $74.537   $74.54   $74.55   $74.50  
  Purchase #7 $136.70   11.230%   $152.0514   $152.05   $152.05   $152.10  
  7 purchase totals = $665.35       $730.8512   $730.85   $730.90   $730.80