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 $246.41   11.405%   $274.5131   $274.51   $274.50   $274.50  
  Purchase #2 $86.79   8.249%   $93.9493   $93.95   $93.95   $93.90  
  Purchase #3 $61.81   10.348%   $68.2061   $68.21   $68.20   $68.20  
  Purchase #4 $114.84   8.712%   $124.8449   $124.84   $124.85   $124.80  
  Purchase #5 $106.98   8.186%   $115.7374   $115.74   $115.75   $115.70  
  Purchase #6 $120.53   6.575%   $128.4548   $128.45   $128.45   $128.50  
  Purchase #7 $150.58   3.352%   $155.6274   $155.63   $155.65   $155.60  
  7 purchase totals = $887.94       $961.3330   $961.33   $961.35   $961.20