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 $68.41   8.599%   $74.2926   $74.29   $74.30   $74.30  
  Purchase #2 $231.81   13.459%   $263.0093   $263.01   $263.00   $263.00  
  Purchase #3 $168.76   3.410%   $174.5147   $174.51   $174.50   $174.50  
  Purchase #4 $118.79   6.362%   $126.3474   $126.35   $126.35   $126.30  
  Purchase #5 $114.65   10.804%   $127.0368   $127.04   $127.05   $127.00  
  Purchase #6 $195.80   13.219%   $221.6828   $221.68   $221.70   $221.70  
  Purchase #7 $21.45   5.679%   $22.6681   $22.67   $22.65   $22.70  
  7 purchase totals = $919.67       $1,009.5517   $1,009.55   $1,009.55   $1,009.50