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 $8.50   7.323%   $9.1225   $9.12   $9.10   $9.10  
  Purchase #2 $76.64   4.490%   $80.0811   $80.08   $80.10   $80.10  
  Purchase #3 $165.99   5.490%   $175.1029   $175.10   $175.10   $175.10  
  Purchase #4 $75.72   7.686%   $81.5398   $81.54   $81.55   $81.50  
  Purchase #5 $79.42   7.732%   $85.5608   $85.56   $85.55   $85.60  
  Purchase #6 $226.39   9.740%   $248.4404   $248.44   $248.45   $248.40  
  Purchase #7 $52.87   6.693%   $56.4086   $56.41   $56.40   $56.40  
  7 purchase totals = $685.53       $736.2561   $736.25   $736.25   $736.20