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 $49.61   6.159%   $52.6655   $52.67   $52.65   $52.70  
  Purchase #2 $166.40   6.123%   $176.5887   $176.59   $176.60   $176.60  
  Purchase #3 $230.83   10.721%   $255.5773   $255.58   $255.60   $255.60  
  Purchase #4 $96.88   11.612%   $108.1297   $108.13   $108.15   $108.10  
  Purchase #5 $114.93   13.195%   $130.095   $130.10   $130.10   $130.10  
  Purchase #6 $210.25   9.552%   $230.3331   $230.33   $230.35   $230.30  
  Purchase #7 $61.80   13.850%   $70.3593   $70.36   $70.35   $70.40  
  7 purchase totals = $930.70       $1,023.7486   $1,023.76   $1,023.80   $1,023.80