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 $244.25   3.823%   $253.5877   $253.59   $253.60   $253.60  
  Purchase #2 $77.92   13.607%   $88.5226   $88.52   $88.50   $88.50  
  Purchase #3 $25.96   5.477%   $27.3818   $27.38   $27.40   $27.40  
  Purchase #4 $250.88   3.349%   $259.282   $259.28   $259.30   $259.30  
  Purchase #5 $162.87   4.795%   $170.6796   $170.68   $170.70   $170.70  
  Purchase #6 $206.34   3.810%   $214.2016   $214.20   $214.20   $214.20  
  Purchase #7 $218.56   9.407%   $239.1199   $239.12   $239.10   $239.10  
  7 purchase totals = $1,186.78       $1,252.7752   $1,252.77   $1,252.80   $1,252.80