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 $218.46   8.737%   $237.5469   $237.55   $237.55   $237.50  
  Purchase #2 $248.37   8.180%   $268.6867   $268.69   $268.70   $268.70  
  Purchase #3 $64.54   8.583%   $70.0795   $70.08   $70.10   $70.10  
  Purchase #4 $188.98   6.340%   $200.9613   $200.96   $200.95   $201.00  
  Purchase #5 $239.71   7.353%   $257.3359   $257.34   $257.35   $257.30  
  Purchase #6 $113.99   5.453%   $120.2059   $120.21   $120.20   $120.20  
  Purchase #7 $200.97   3.259%   $207.5196   $207.52   $207.50   $207.50  
  7 purchase totals = $1,275.02       $1,362.3358   $1,362.35   $1,362.35   $1,362.30