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 $61.55   6.542%   $65.5766   $65.58   $65.60   $65.60  
  Purchase #2 $181.64   9.115%   $198.1965   $198.20   $198.20   $198.20  
  Purchase #3 $137.53   13.553%   $156.1694   $156.17   $156.15   $156.20  
  Purchase #4 $250.30   5.408%   $263.8362   $263.84   $263.85   $263.80  
  Purchase #5 $114.28   3.258%   $118.0032   $118.00   $118.00   $118.00  
  Purchase #6 $79.80   4.789%   $83.6216   $83.62   $83.60   $83.60  
  Purchase #7 $61.49   5.225%   $64.7029   $64.70   $64.70   $64.70  
  7 purchase totals = $886.59       $950.1064   $950.11   $950.10   $950.10