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 $84.60   12.435%   $95.12   $95.12   $95.10   $95.10  
  Purchase #2 $203.98   8.798%   $221.9262   $221.93   $221.95   $221.90  
  Purchase #3 $125.78   6.353%   $133.7708   $133.77   $133.75   $133.80  
  Purchase #4 $246.28   8.194%   $266.4602   $266.46   $266.45   $266.50  
  Purchase #5 $92.59   13.435%   $105.0295   $105.03   $105.05   $105.00  
  Purchase #6 $60.97   10.256%   $67.2231   $67.22   $67.20   $67.20  
  Purchase #7 $167.32   12.758%   $188.6667   $188.67   $188.65   $188.70  
  7 purchase totals = $981.52       $1,078.1965   $1,078.20   $1,078.15   $1,078.20