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 $99.59   8.382%   $107.9376   $107.94   $107.95   $107.90  
  Purchase #2 $68.29   7.308%   $73.2806   $73.28   $73.30   $73.30  
  Purchase #3 $202.30   9.331%   $221.1766   $221.18   $221.20   $221.20  
  Purchase #4 $246.39   9.282%   $269.2599   $269.26   $269.25   $269.30  
  Purchase #5 $69.63   9.229%   $76.0562   $76.06   $76.05   $76.10  
  Purchase #6 $170.50   10.213%   $187.9132   $187.91   $187.90   $187.90  
  Purchase #7 $60.30   13.718%   $68.572   $68.57   $68.55   $68.60  
  7 purchase totals = $917.00       $1,004.1961   $1,004.20   $1,004.20   $1,004.30