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 $88.29   11.719%   $98.6367   $98.64   $98.65   $98.60  
  Purchase #2 $134.25   12.482%   $151.0071   $151.01   $151.00   $151.00  
  Purchase #3 $114.71   12.195%   $128.6989   $128.70   $128.70   $128.70  
  Purchase #4 $195.94   3.628%   $203.0487   $203.05   $203.05   $203.00  
  Purchase #5 $250.48   6.855%   $267.6504   $267.65   $267.65   $267.70  
  Purchase #6 $86.99   13.693%   $98.9015   $98.90   $98.90   $98.90  
  Purchase #7 $138.56   8.548%   $150.4041   $150.40   $150.40   $150.40  
  7 purchase totals = $1,009.22       $1,098.3474   $1,098.35   $1,098.35   $1,098.30