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 $46.88   6.672%   $50.0078   $50.01   $50.00   $50.00  
  Purchase #2 $214.25   8.471%   $232.3991   $232.40   $232.40   $232.40  
  Purchase #3 $109.34   4.220%   $113.9541   $113.95   $113.95   $114.00  
  Purchase #4 $81.34   5.215%   $85.5819   $85.58   $85.60   $85.60  
  Purchase #5 $215.80   11.125%   $239.8078   $239.81   $239.80   $239.80  
  Purchase #6 $153.99   5.729%   $162.8121   $162.81   $162.80   $162.80  
  Purchase #7 $157.83   5.860%   $167.0788   $167.08   $167.10   $167.10  
  7 purchase totals = $979.43       $1,051.6416   $1,051.64   $1,051.65   $1,051.70