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 $182.72   13.182%   $206.8062   $206.81   $206.80   $206.80  
  Purchase #2 $71.34   11.693%   $79.6818   $79.68   $79.70   $79.70  
  Purchase #3 $50.54   3.404%   $52.2604   $52.26   $52.25   $52.30  
  Purchase #4 $82.83   4.565%   $86.6112   $86.61   $86.60   $86.60  
  Purchase #5 $240.46   12.702%   $271.0032   $271.00   $271.00   $271.00  
  Purchase #6 $54.68   11.566%   $61.0043   $61.00   $61.00   $61.00  
  Purchase #7 $246.27   4.184%   $256.5739   $256.57   $256.55   $256.60  
  7 purchase totals = $928.84       $1,013.9410   $1,013.93   $1,013.90   $1,014.00