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 $186.36   13.235%   $211.0247   $211.02   $211.00   $211.00  
  Purchase #2 $42.29   9.423%   $46.275   $46.28   $46.30   $46.30  
  Purchase #3 $132.65   9.747%   $145.5794   $145.58   $145.60   $145.60  
  Purchase #4 $181.39   8.182%   $196.2313   $196.23   $196.25   $196.20  
  Purchase #5 $123.66   8.515%   $134.1896   $134.19   $134.20   $134.20  
  Purchase #6 $9.52   5.164%   $10.0116   $10.01   $10.00   $10.00  
  Purchase #7 $211.81   6.103%   $224.7368   $224.74   $224.75   $224.70  
  7 purchase totals = $887.68       $968.0484   $968.05   $968.10   $968.00