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 $23.33   5.239%   $24.5523   $24.55   $24.55   $24.60  
  Purchase #2 $227.65   8.646%   $247.3326   $247.33   $247.35   $247.30  
  Purchase #3 $112.93   6.562%   $120.3405   $120.34   $120.35   $120.30  
  Purchase #4 $10.87   13.208%   $12.3057   $12.31   $12.30   $12.30  
  Purchase #5 $169.55   6.441%   $180.4707   $180.47   $180.45   $180.50  
  Purchase #6 $71.68   8.387%   $77.6918   $77.69   $77.70   $77.70  
  Purchase #7 $241.79   8.438%   $262.1922   $262.19   $262.20   $262.20  
  7 purchase totals = $857.80       $924.8858   $924.88   $924.90   $924.90