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 $50.50   11.583%   $56.3494   $56.35   $56.35   $56.30  
  Purchase #2 $235.62   3.572%   $244.0363   $244.04   $244.05   $244.00  
  Purchase #3 $53.89   13.167%   $60.9857   $60.99   $61.00   $61.00  
  Purchase #4 $124.76   13.186%   $141.2109   $141.21   $141.20   $141.20  
  Purchase #5 $221.45   12.310%   $248.7105   $248.71   $248.70   $248.70  
  Purchase #6 $209.48   11.402%   $233.3649   $233.36   $233.35   $233.40  
  Purchase #7 $66.33   6.507%   $70.6461   $70.65   $70.65   $70.60  
  7 purchase totals = $962.03       $1,055.3038   $1,055.31   $1,055.30   $1,055.20