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 $116.65   8.481%   $126.5431   $126.54   $126.55   $126.50  
  Purchase #2 $153.68   7.866%   $165.7685   $165.77   $165.75   $165.80  
  Purchase #3 $184.27   6.602%   $196.4355   $196.44   $196.45   $196.40  
  Purchase #4 $213.86   7.128%   $229.1039   $229.10   $229.10   $229.10  
  Purchase #5 $34.96   8.762%   $38.0232   $38.02   $38.00   $38.00  
  Purchase #6 $154.26   11.762%   $172.4041   $172.40   $172.40   $172.40  
  Purchase #7 $178.26   13.131%   $201.6673   $201.67   $201.65   $201.70  
  7 purchase totals = $1,035.94       $1,129.9456   $1,129.94   $1,129.90   $1,129.90