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 $65.77   11.553%   $73.3684   $73.37   $73.35   $73.40  
  Purchase #2 $162.92   7.611%   $175.3198   $175.32   $175.30   $175.30  
  Purchase #3 $156.52   13.613%   $177.8271   $177.83   $177.85   $177.80  
  Purchase #4 $56.74   7.773%   $61.1504   $61.15   $61.15   $61.20  
  Purchase #5 $245.75   11.359%   $273.6647   $273.66   $273.65   $273.70  
  Purchase #6 $140.25   9.708%   $153.8655   $153.87   $153.85   $153.90  
  Purchase #7 $68.37   7.654%   $73.603   $73.60   $73.60   $73.60  
  7 purchase totals = $896.32       $988.7989   $988.80   $988.75   $988.90