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 $81.87   3.416%   $84.6667   $84.67   $84.65   $84.70  
  Purchase #2 $81.54   5.692%   $86.1813   $86.18   $86.20   $86.20  
  Purchase #3 $49.74   4.348%   $51.9027   $51.90   $51.90   $51.90  
  Purchase #4 $151.68   9.214%   $165.6558   $165.66   $165.65   $165.70  
  Purchase #5 $96.39   9.210%   $105.2675   $105.27   $105.25   $105.30  
  Purchase #6 $228.65   5.794%   $241.898   $241.90   $241.90   $241.90  
  Purchase #7 $23.99   3.755%   $24.8908   $24.89   $24.90   $24.90  
  7 purchase totals = $713.86       $760.4628   $760.47   $760.45   $760.60