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 $242.50   10.407%   $267.737   $267.74   $267.75   $267.70  
  Purchase #2 $77.61   6.187%   $82.4117   $82.41   $82.40   $82.40  
  Purchase #3 $169.79   5.743%   $179.541   $179.54   $179.55   $179.50  
  Purchase #4 $48.52   9.339%   $53.0513   $53.05   $53.05   $53.10  
  Purchase #5 $77.38   11.212%   $86.0558   $86.06   $86.05   $86.10  
  Purchase #6 $223.28   11.369%   $248.6647   $248.66   $248.65   $248.70  
  Purchase #7 $49.53   13.631%   $56.2814   $56.28   $56.30   $56.30  
  7 purchase totals = $888.61       $973.7429   $973.74   $973.75   $973.80