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 $182.83   10.769%   $202.519   $202.52   $202.50   $202.50  
  Purchase #2 $113.52   11.549%   $126.6304   $126.63   $126.65   $126.60  
  Purchase #3 $177.42   3.870%   $184.2862   $184.29   $184.30   $184.30  
  Purchase #4 $235.31   3.230%   $242.9105   $242.91   $242.90   $242.90  
  Purchase #5 $54.97   12.136%   $61.6412   $61.64   $61.65   $61.60  
  Purchase #6 $77.30   6.539%   $82.3546   $82.35   $82.35   $82.40  
  Purchase #7 $74.79   9.577%   $81.9526   $81.95   $81.95   $82.00  
  7 purchase totals = $916.14       $982.2945   $982.29   $982.30   $982.30