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 $161.34   13.245%   $182.7095   $182.71   $182.70   $182.70  
  Purchase #2 $77.48   11.152%   $86.1206   $86.12   $86.10   $86.10  
  Purchase #3 $116.36   4.705%   $121.8347   $121.83   $121.85   $121.80  
  Purchase #4 $121.78   3.828%   $126.4417   $126.44   $126.45   $126.40  
  Purchase #5 $111.86   12.681%   $126.045   $126.05   $126.05   $126.00  
  Purchase #6 $108.96   12.212%   $122.2662   $122.27   $122.25   $122.30  
  Purchase #7 $169.88   12.833%   $191.6807   $191.68   $191.70   $191.70  
  7 purchase totals = $867.66       $957.0984   $957.10   $957.10   $957.00