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 $60.28   9.255%   $65.8589   $65.86   $65.85   $65.90  
  Purchase #2 $179.70   6.156%   $190.7623   $190.76   $190.75   $190.80  
  Purchase #3 $115.67   4.831%   $121.258   $121.26   $121.25   $121.30  
  Purchase #4 $159.80   8.314%   $173.0858   $173.09   $173.10   $173.10  
  Purchase #5 $182.90   6.564%   $194.9056   $194.91   $194.90   $194.90  
  Purchase #6 $90.45   5.368%   $95.3054   $95.31   $95.30   $95.30  
  Purchase #7 $36.52   7.834%   $39.381   $39.38   $39.40   $39.40  
  7 purchase totals = $825.32       $880.5570   $880.57   $880.55   $880.70