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 $169.56   13.532%   $192.5049   $192.50   $192.50   $192.50  
  Purchase #2 $55.94   6.249%   $59.4357   $59.44   $59.45   $59.40  
  Purchase #3 $238.55   11.451%   $265.8664   $265.87   $265.85   $265.90  
  Purchase #4 $24.72   8.393%   $26.7947   $26.79   $26.80   $26.80  
  Purchase #5 $115.87   10.177%   $127.6621   $127.66   $127.65   $127.70  
  Purchase #6 $123.26   10.172%   $135.798   $135.80   $135.80   $135.80  
  Purchase #7 $60.32   8.866%   $65.668   $65.67   $65.65   $65.70  
  7 purchase totals = $788.22       $873.7298   $873.73   $873.70   $873.80