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 $203.51   6.539%   $216.8175   $216.82   $216.80   $216.80  
  Purchase #2 $87.71   9.253%   $95.8258   $95.83   $95.85   $95.80  
  Purchase #3 $88.73   10.836%   $98.3448   $98.34   $98.35   $98.30  
  Purchase #4 $71.52   6.366%   $76.073   $76.07   $76.05   $76.10  
  Purchase #5 $207.77   13.268%   $235.3369   $235.34   $235.35   $235.30  
  Purchase #6 $127.57   9.547%   $139.7491   $139.75   $139.75   $139.70  
  Purchase #7 $116.30   5.488%   $122.6825   $122.68   $122.70   $122.70  
  7 purchase totals = $903.11       $984.8296   $984.83   $984.85   $984.70