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 $208.54   11.499%   $232.52   $232.52   $232.50   $232.50  
  Purchase #2 $202.69   11.130%   $225.2494   $225.25   $225.25   $225.20  
  Purchase #3 $70.65   12.382%   $79.3979   $79.40   $79.40   $79.40  
  Purchase #4 $209.68   10.569%   $231.8411   $231.84   $231.85   $231.80  
  Purchase #5 $193.33   5.316%   $203.6074   $203.61   $203.60   $203.60  
  Purchase #6 $225.92   8.850%   $245.9139   $245.91   $245.90   $245.90  
  Purchase #7 $100.46   12.295%   $112.8116   $112.81   $112.80   $112.80  
  7 purchase totals = $1,211.27       $1,331.3413   $1,331.34   $1,331.30   $1,331.20