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 $49.46   12.621%   $55.7023   $55.70   $55.70   $55.70  
  Purchase #2 $117.32   8.114%   $126.8393   $126.84   $126.85   $126.80  
  Purchase #3 $73.73   8.784%   $80.2064   $80.21   $80.20   $80.20  
  Purchase #4 $68.84   8.492%   $74.6859   $74.69   $74.70   $74.70  
  Purchase #5 $160.80   11.715%   $179.6377   $179.64   $179.65   $179.60  
  Purchase #6 $100.26   3.178%   $103.4463   $103.45   $103.45   $103.40  
  Purchase #7 $144.91   7.858%   $156.297   $156.30   $156.30   $156.30  
  7 purchase totals = $715.32       $776.8149   $776.83   $776.85   $776.70