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 $49.97   4.546%   $52.2416   $52.24   $52.25   $52.20  
  Purchase #2 $230.82   4.149%   $240.3967   $240.40   $240.40   $240.40  
  Purchase #3 $140.70   9.195%   $153.6374   $153.64   $153.65   $153.60  
  Purchase #4 $185.96   6.249%   $197.5806   $197.58   $197.60   $197.60  
  Purchase #5 $200.98   3.496%   $208.0063   $208.01   $208.00   $208.00  
  Purchase #6 $20.75   10.302%   $22.8877   $22.89   $22.90   $22.90  
  Purchase #7 $162.44   6.829%   $173.533   $173.53   $173.55   $173.50  
  7 purchase totals = $991.62       $1,048.2833   $1,048.29   $1,048.35   $1,048.20