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 $74.30   6.563%   $79.1763   $79.18   $79.20   $79.20  
  Purchase #2 $111.63   13.610%   $126.8228   $126.82   $126.80   $126.80  
  Purchase #3 $234.78   13.785%   $267.1444   $267.14   $267.15   $267.10  
  Purchase #4 $24.62   5.653%   $26.0118   $26.01   $26.00   $26.00  
  Purchase #5 $80.48   4.685%   $84.2505   $84.25   $84.25   $84.30  
  Purchase #6 $174.57   10.596%   $193.0674   $193.07   $193.05   $193.10  
  Purchase #7 $222.31   10.334%   $245.2835   $245.28   $245.30   $245.30  
  7 purchase totals = $922.69       $1,021.7567   $1,021.75   $1,021.75   $1,021.80