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 $198.84   11.654%   $222.0128   $222.01   $222.00   $222.00  
  Purchase #2 $65.38   7.737%   $70.4385   $70.44   $70.45   $70.40  
  Purchase #3 $54.55   3.248%   $56.3218   $56.32   $56.30   $56.30  
  Purchase #4 $103.97   12.399%   $116.8612   $116.86   $116.85   $116.90  
  Purchase #5 $179.99   7.151%   $192.8611   $192.86   $192.85   $192.90  
  Purchase #6 $36.83   8.103%   $39.8143   $39.81   $39.80   $39.80  
  Purchase #7 $244.49   5.278%   $257.3942   $257.39   $257.40   $257.40  
  7 purchase totals = $884.05       $955.7039   $955.69   $955.65   $955.70