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 $164.25   8.770%   $178.6547   $178.65   $178.65   $178.70  
  Purchase #2 $146.89   11.246%   $163.4092   $163.41   $163.40   $163.40  
  Purchase #3 $37.56   11.246%   $41.784   $41.78   $41.80   $41.80  
  Purchase #4 $235.58   7.665%   $253.6372   $253.64   $253.65   $253.60  
  Purchase #5 $173.26   7.266%   $185.8491   $185.85   $185.85   $185.80  
  Purchase #6 $56.99   5.753%   $60.2686   $60.27   $60.25   $60.30  
  Purchase #7 $46.38   13.743%   $52.754   $52.75   $52.75   $52.80  
  7 purchase totals = $860.91       $936.3568   $936.35   $936.35   $936.40