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 $161.67   13.617%   $183.6846   $183.68   $183.70   $183.70  
  Purchase #2 $57.60   13.174%   $65.1882   $65.19   $65.20   $65.20  
  Purchase #3 $94.55   6.351%   $100.5549   $100.55   $100.55   $100.60  
  Purchase #4 $106.52   8.688%   $115.7745   $115.77   $115.75   $115.80  
  Purchase #5 $56.75   6.358%   $60.3582   $60.36   $60.35   $60.40  
  Purchase #6 $24.74   11.435%   $27.569   $27.57   $27.55   $27.60  
  Purchase #7 $166.86   9.373%   $182.4998   $182.50   $182.50   $182.50  
  7 purchase totals = $668.69       $735.6292   $735.62   $735.60   $735.80