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 $158.59   12.704%   $178.7373   $178.74   $178.75   $178.70  
  Purchase #2 $247.25   11.187%   $274.9099   $274.91   $274.90   $274.90  
  Purchase #3 $30.67   8.823%   $33.376   $33.38   $33.40   $33.40  
  Purchase #4 $167.60   13.638%   $190.4573   $190.46   $190.45   $190.50  
  Purchase #5 $44.68   3.557%   $46.2693   $46.27   $46.25   $46.30  
  Purchase #6 $81.99   13.394%   $92.9717   $92.97   $92.95   $93.00  
  Purchase #7 $245.58   4.194%   $255.8796   $255.88   $255.90   $255.90  
  7 purchase totals = $976.36       $1,072.6011   $1,072.61   $1,072.60   $1,072.70