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 $88.69   8.553%   $96.2757   $96.28   $96.30   $96.30  
  Purchase #2 $143.34   4.459%   $149.7315   $149.73   $149.75   $149.70  
  Purchase #3 $222.89   13.293%   $252.5188   $252.52   $252.50   $252.50  
  Purchase #4 $180.89   6.459%   $192.5737   $192.57   $192.55   $192.60  
  Purchase #5 $213.40   8.232%   $230.9671   $230.97   $230.95   $231.00  
  Purchase #6 $161.77   7.647%   $174.1406   $174.14   $174.15   $174.10  
  Purchase #7 $114.59   3.207%   $118.2649   $118.26   $118.25   $118.30  
  7 purchase totals = $1,125.57       $1,214.4723   $1,214.47   $1,214.45   $1,214.50