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 $215.41   9.124%   $235.064   $235.06   $235.05   $235.10  
  Purchase #2 $160.38   8.276%   $173.653   $173.65   $173.65   $173.70  
  Purchase #3 $53.88   5.150%   $56.6548   $56.65   $56.65   $56.70  
  Purchase #4 $96.80   9.488%   $105.9844   $105.98   $106.00   $106.00  
  Purchase #5 $99.36   13.236%   $112.5113   $112.51   $112.50   $112.50  
  Purchase #6 $103.76   13.352%   $117.614   $117.61   $117.60   $117.60  
  Purchase #7 $161.83   9.716%   $177.5534   $177.55   $177.55   $177.60  
  7 purchase totals = $891.42       $979.0349   $979.01   $979.00   $979.20