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 $49.78   10.391%   $54.9526   $54.95   $54.95   $55.00  
  Purchase #2 $203.84   10.228%   $224.6888   $224.69   $224.70   $224.70  
  Purchase #3 $248.68   4.636%   $260.2088   $260.21   $260.20   $260.20  
  Purchase #4 $86.80   13.784%   $98.7645   $98.76   $98.75   $98.80  
  Purchase #5 $106.49   6.689%   $113.6131   $113.61   $113.60   $113.60  
  Purchase #6 $244.52   8.820%   $266.0867   $266.09   $266.10   $266.10  
  Purchase #7 $59.85   10.605%   $66.1971   $66.20   $66.20   $66.20  
  7 purchase totals = $999.96       $1,084.5116   $1,084.51   $1,084.50   $1,084.60