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 $60.86   7.441%   $65.3886   $65.39   $65.40   $65.40  
  Purchase #2 $35.88   5.744%   $37.9409   $37.94   $37.95   $37.90  
  Purchase #3 $192.66   4.718%   $201.7497   $201.75   $201.75   $201.70  
  Purchase #4 $100.81   12.763%   $113.6764   $113.68   $113.70   $113.70  
  Purchase #5 $53.93   11.348%   $60.05   $60.05   $60.05   $60.10  
  Purchase #6 $48.64   7.270%   $52.1761   $52.18   $52.20   $52.20  
  Purchase #7 $73.95   8.448%   $80.1973   $80.20   $80.20   $80.20  
  7 purchase totals = $566.73       $611.1790   $611.19   $611.25   $611.20