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 $61.84   13.294%   $70.061   $70.06   $70.05   $70.10  
  Purchase #2 $169.34   8.835%   $184.3012   $184.30   $184.30   $184.30  
  Purchase #3 $114.88   4.441%   $119.9818   $119.98   $120.00   $120.00  
  Purchase #4 $68.39   7.836%   $73.749   $73.75   $73.75   $73.70  
  Purchase #5 $127.71   9.107%   $139.3405   $139.34   $139.35   $139.30  
  Purchase #6 $208.77   5.349%   $219.9371   $219.94   $219.95   $219.90  
  Purchase #7 $245.70   9.834%   $269.8621   $269.86   $269.85   $269.90  
  7 purchase totals = $996.63       $1,077.2327   $1,077.23   $1,077.25   $1,077.20