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 $216.82   11.401%   $241.5396   $241.54   $241.55   $241.50  
  Purchase #2 $186.87   13.462%   $212.0264   $212.03   $212.05   $212.00  
  Purchase #3 $60.84   10.476%   $67.2136   $67.21   $67.20   $67.20  
  Purchase #4 $71.64   3.489%   $74.1395   $74.14   $74.15   $74.10  
  Purchase #5 $103.49   3.453%   $107.0635   $107.06   $107.05   $107.10  
  Purchase #6 $28.37   5.124%   $29.8237   $29.82   $29.80   $29.80  
  Purchase #7 $40.79   9.243%   $44.5602   $44.56   $44.55   $44.60  
  7 purchase totals = $708.82       $776.3665   $776.36   $776.35   $776.30