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 $88.64   5.579%   $93.5852   $93.59   $93.60   $93.60  
  Purchase #2 $33.45   7.309%   $35.8949   $35.89   $35.90   $35.90  
  Purchase #3 $220.80   8.134%   $238.7599   $238.76   $238.75   $238.80  
  Purchase #4 $224.72   8.317%   $243.41   $243.41   $243.40   $243.40  
  Purchase #5 $13.85   3.531%   $14.339   $14.34   $14.35   $14.30  
  Purchase #6 $27.52   11.570%   $30.7041   $30.70   $30.70   $30.70  
  Purchase #7 $15.73   5.418%   $16.5823   $16.58   $16.60   $16.60  
  7 purchase totals = $624.71       $673.2754   $673.27   $673.30   $673.30