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 $52.35   8.271%   $56.6799   $56.68   $56.70   $56.70  
  Purchase #2 $26.25   13.322%   $29.747   $29.75   $29.75   $29.70  
  Purchase #3 $138.49   10.770%   $153.4054   $153.41   $153.40   $153.40  
  Purchase #4 $73.88   4.465%   $77.1787   $77.18   $77.20   $77.20  
  Purchase #5 $47.65   6.395%   $50.6972   $50.70   $50.70   $50.70  
  Purchase #6 $150.59   12.849%   $169.9393   $169.94   $169.95   $169.90  
  Purchase #7 $203.53   4.152%   $211.9806   $211.98   $212.00   $212.00  
  7 purchase totals = $692.74       $749.6281   $749.64   $749.70   $749.60