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 $74.91   11.293%   $83.3696   $83.37   $83.35   $83.40  
  Purchase #2 $118.80   12.764%   $133.9636   $133.96   $133.95   $134.00  
  Purchase #3 $190.67   3.852%   $198.0146   $198.01   $198.00   $198.00  
  Purchase #4 $117.81   13.189%   $133.348   $133.35   $133.35   $133.30  
  Purchase #5 $195.50   9.638%   $214.3423   $214.34   $214.35   $214.30  
  Purchase #6 $181.95   6.446%   $193.6785   $193.68   $193.70   $193.70  
  Purchase #7 $9.64   10.363%   $10.639   $10.64   $10.65   $10.60  
  7 purchase totals = $889.28       $967.3556   $967.35   $967.35   $967.30