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 $49.80   8.794%   $54.1794   $54.18   $54.20   $54.20  
  Purchase #2 $179.51   4.123%   $186.9112   $186.91   $186.90   $186.90  
  Purchase #3 $28.26   13.239%   $32.0013   $32.00   $32.00   $32.00  
  Purchase #4 $56.48   7.222%   $60.559   $60.56   $60.55   $60.60  
  Purchase #5 $67.25   10.397%   $74.242   $74.24   $74.25   $74.20  
  Purchase #6 $197.70   6.737%   $211.019   $211.02   $211.00   $211.00  
  Purchase #7 $69.68   5.814%   $73.7312   $73.73   $73.75   $73.70  
  7 purchase totals = $648.68       $692.6431   $692.64   $692.65   $692.60