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 $106.43   7.845%   $114.7794   $114.78   $114.80   $114.80  
  Purchase #2 $182.42   11.203%   $202.8565   $202.86   $202.85   $202.90  
  Purchase #3 $230.78   5.510%   $243.496   $243.50   $243.50   $243.50  
  Purchase #4 $248.49   9.163%   $271.2591   $271.26   $271.25   $271.30  
  Purchase #5 $29.70   13.160%   $33.6085   $33.61   $33.60   $33.60  
  Purchase #6 $181.37   3.212%   $187.1956   $187.20   $187.20   $187.20  
  Purchase #7 $174.36   13.748%   $198.331   $198.33   $198.35   $198.30  
  7 purchase totals = $1,153.55       $1,251.5261   $1,251.54   $1,251.55   $1,251.60