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 $128.94   11.647%   $143.9576   $143.96   $143.95   $144.00  
  Purchase #2 $42.92   6.830%   $45.8514   $45.85   $45.85   $45.90  
  Purchase #3 $172.26   8.154%   $186.3061   $186.31   $186.30   $186.30  
  Purchase #4 $41.44   3.692%   $42.97   $42.97   $42.95   $43.00  
  Purchase #5 $231.35   9.754%   $253.9159   $253.92   $253.90   $253.90  
  Purchase #6 $186.81   10.648%   $206.7015   $206.70   $206.70   $206.70  
  Purchase #7 $163.50   11.664%   $182.5706   $182.57   $182.55   $182.60  
  7 purchase totals = $967.22       $1,062.2731   $1,062.28   $1,062.20   $1,062.40