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 $54.46   5.149%   $57.2641   $57.26   $57.25   $57.30  
  Purchase #2 $165.47   11.727%   $184.8747   $184.87   $184.85   $184.90  
  Purchase #3 $186.48   13.359%   $211.3919   $211.39   $211.40   $211.40  
  Purchase #4 $30.81   13.291%   $34.905   $34.91   $34.90   $34.90  
  Purchase #5 $70.49   3.298%   $72.8148   $72.81   $72.80   $72.80  
  Purchase #6 $186.95   8.310%   $202.4855   $202.49   $202.50   $202.50  
  Purchase #7 $80.77   9.698%   $88.6031   $88.60   $88.60   $88.60  
  7 purchase totals = $775.43       $852.3391   $852.33   $852.30   $852.40