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 $90.78   13.579%   $103.107   $103.11   $103.10   $103.10  
  Purchase #2 $161.94   6.657%   $172.7203   $172.72   $172.70   $172.70  
  Purchase #3 $182.80   13.675%   $207.7979   $207.80   $207.80   $207.80  
  Purchase #4 $28.25   7.766%   $30.4439   $30.44   $30.45   $30.40  
  Purchase #5 $122.72   10.150%   $135.1761   $135.18   $135.20   $135.20  
  Purchase #6 $52.52   12.273%   $58.9658   $58.97   $58.95   $59.00  
  Purchase #7 $20.78   12.106%   $23.2956   $23.30   $23.30   $23.30  
  7 purchase totals = $659.79       $731.5066   $731.52   $731.50   $731.50