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 $169.49   3.121%   $174.7798   $174.78   $174.80   $174.80  
  Purchase #2 $229.68   13.641%   $261.0106   $261.01   $261.00   $261.00  
  Purchase #3 $228.69   8.794%   $248.801   $248.80   $248.80   $248.80  
  Purchase #4 $74.44   11.377%   $82.909   $82.91   $82.90   $82.90  
  Purchase #5 $199.42   11.119%   $221.5935   $221.59   $221.60   $221.60  
  Purchase #6 $188.52   7.706%   $203.0474   $203.05   $203.05   $203.00  
  Purchase #7 $55.60   10.123%   $61.2284   $61.23   $61.25   $61.20  
  7 purchase totals = $1,145.84       $1,253.3697   $1,253.37   $1,253.40   $1,253.30