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 $126.32   6.599%   $134.6559   $134.66   $134.65   $134.70  
  Purchase #2 $56.96   11.714%   $63.6323   $63.63   $63.65   $63.60  
  Purchase #3 $97.94   7.479%   $105.2649   $105.26   $105.25   $105.30  
  Purchase #4 $204.77   8.339%   $221.8458   $221.85   $221.85   $221.80  
  Purchase #5 $91.51   12.821%   $103.2425   $103.24   $103.25   $103.20  
  Purchase #6 $187.89   11.132%   $208.8059   $208.81   $208.80   $208.80  
  Purchase #7 $153.26   6.324%   $162.9522   $162.95   $162.95   $163.00  
  7 purchase totals = $918.65       $1,000.3995   $1,000.40   $1,000.40   $1,000.40