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 $191.50   8.246%   $207.2911   $207.29   $207.30   $207.30  
  Purchase #2 $69.71   5.140%   $73.2931   $73.29   $73.30   $73.30  
  Purchase #3 $81.51   6.262%   $86.6142   $86.61   $86.60   $86.60  
  Purchase #4 $237.69   3.278%   $245.4815   $245.48   $245.50   $245.50  
  Purchase #5 $160.90   6.293%   $171.0254   $171.03   $171.05   $171.00  
  Purchase #6 $113.40   8.172%   $122.667   $122.67   $122.65   $122.70  
  Purchase #7 $72.69   6.644%   $77.5195   $77.52   $77.50   $77.50  
  7 purchase totals = $927.40       $983.8918   $983.89   $983.90   $983.90