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 $52.36   11.268%   $58.2599   $58.26   $58.25   $58.30  
  Purchase #2 $157.69   13.239%   $178.5666   $178.57   $178.55   $178.60  
  Purchase #3 $113.52   13.356%   $128.6817   $128.68   $128.70   $128.70  
  Purchase #4 $201.57   11.179%   $224.1035   $224.10   $224.10   $224.10  
  Purchase #5 $115.28   5.831%   $122.002   $122.00   $122.00   $122.00  
  Purchase #6 $89.78   3.494%   $92.9169   $92.92   $92.90   $92.90  
  Purchase #7 $42.72   11.646%   $47.6952   $47.70   $47.70   $47.70  
  7 purchase totals = $772.92       $852.2258   $852.23   $852.20   $852.30