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 $82.33   13.270%   $93.2552   $93.26   $93.25   $93.30  
  Purchase #2 $102.79   9.542%   $112.5982   $112.60   $112.60   $112.60  
  Purchase #3 $162.62   8.622%   $176.6411   $176.64   $176.65   $176.60  
  Purchase #4 $192.64   10.326%   $212.532   $212.53   $212.55   $212.50  
  Purchase #5 $37.44   11.833%   $41.8703   $41.87   $41.85   $41.90  
  Purchase #6 $19.77   8.862%   $21.522   $21.52   $21.50   $21.50  
  Purchase #7 $248.45   12.771%   $280.1795   $280.18   $280.20   $280.20  
  7 purchase totals = $846.04       $938.5983   $938.60   $938.60   $938.60