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 $61.49   13.424%   $69.7444   $69.74   $69.75   $69.70  
  Purchase #2 $239.32   12.740%   $269.8094   $269.81   $269.80   $269.80  
  Purchase #3 $192.83   7.810%   $207.89   $207.89   $207.90   $207.90  
  Purchase #4 $187.32   8.616%   $203.4595   $203.46   $203.45   $203.50  
  Purchase #5 $110.64   11.835%   $123.7342   $123.73   $123.75   $123.70  
  Purchase #6 $242.27   4.171%   $252.3751   $252.38   $252.40   $252.40  
  Purchase #7 $221.85   11.813%   $248.0571   $248.06   $248.05   $248.10  
  7 purchase totals = $1,255.72       $1,375.0697   $1,375.07   $1,375.10   $1,375.10