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 $199.55   3.713%   $206.9593   $206.96   $206.95   $207.00  
  Purchase #2 $226.61   3.677%   $234.9424   $234.94   $234.95   $234.90  
  Purchase #3 $41.52   3.578%   $43.0056   $43.01   $43.00   $43.00  
  Purchase #4 $159.64   3.677%   $165.51   $165.51   $165.50   $165.50  
  Purchase #5 $34.57   12.795%   $38.9932   $38.99   $39.00   $39.00  
  Purchase #6 $224.77   7.529%   $241.6929   $241.69   $241.70   $241.70  
  Purchase #7 $142.68   13.809%   $162.3827   $162.38   $162.40   $162.40  
  7 purchase totals = $1,029.34       $1,093.4861   $1,093.48   $1,093.50   $1,093.50