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 $49.30   11.211%   $54.827   $54.83   $54.85   $54.80  
  Purchase #2 $153.27   5.852%   $162.2394   $162.24   $162.25   $162.20  
  Purchase #3 $5.52   7.453%   $5.9314   $5.93   $5.95   $5.90  
  Purchase #4 $241.25   10.645%   $266.9311   $266.93   $266.95   $266.90  
  Purchase #5 $115.94   9.228%   $126.6389   $126.64   $126.65   $126.60  
  Purchase #6 $131.86   6.232%   $140.0775   $140.08   $140.10   $140.10  
  Purchase #7 $63.55   7.775%   $68.491   $68.49   $68.50   $68.50  
  7 purchase totals = $760.69       $825.1363   $825.14   $825.25   $825.00