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 $64.61   9.850%   $70.9741   $70.97   $70.95   $71.00  
  Purchase #2 $148.88   12.140%   $166.954   $166.95   $166.95   $167.00  
  Purchase #3 $118.48   6.491%   $126.1705   $126.17   $126.15   $126.20  
  Purchase #4 $241.98   4.226%   $252.2061   $252.21   $252.20   $252.20  
  Purchase #5 $183.82   4.650%   $192.3676   $192.37   $192.35   $192.40  
  Purchase #6 $124.77   13.524%   $141.6439   $141.64   $141.65   $141.60  
  Purchase #7 $98.93   13.159%   $111.9482   $111.95   $111.95   $111.90  
  7 purchase totals = $981.47       $1,062.2644   $1,062.26   $1,062.20   $1,062.30