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 $235.67   5.357%   $248.2948   $248.29   $248.30   $248.30  
  Purchase #2 $96.80   10.129%   $106.6049   $106.60   $106.60   $106.60  
  Purchase #3 $116.99   8.830%   $127.3202   $127.32   $127.30   $127.30  
  Purchase #4 $150.39   12.331%   $168.9346   $168.93   $168.95   $168.90  
  Purchase #5 $29.60   11.520%   $33.0099   $33.01   $33.00   $33.00  
  Purchase #6 $203.25   6.386%   $216.2295   $216.23   $216.25   $216.20  
  Purchase #7 $47.93   10.398%   $52.9138   $52.91   $52.90   $52.90  
  7 purchase totals = $880.63       $953.3077   $953.29   $953.30   $953.20