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 $39.69   9.557%   $43.4832   $43.48   $43.50   $43.50  
  Purchase #2 $67.87   13.744%   $77.1981   $77.20   $77.20   $77.20  
  Purchase #3 $86.90   5.118%   $91.3475   $91.35   $91.35   $91.30  
  Purchase #4 $174.61   9.527%   $191.2451   $191.25   $191.25   $191.20  
  Purchase #5 $48.82   8.398%   $52.9199   $52.92   $52.90   $52.90  
  Purchase #6 $67.50   10.448%   $74.5524   $74.55   $74.55   $74.60  
  Purchase #7 $209.30   13.127%   $236.7748   $236.77   $236.75   $236.80  
  7 purchase totals = $694.69       $767.5210   $767.52   $767.50   $767.50