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 $58.77   5.638%   $62.0835   $62.08   $62.10   $62.10  
  Purchase #2 $81.90   3.589%   $84.8394   $84.84   $84.85   $84.80  
  Purchase #3 $166.28   8.232%   $179.9682   $179.97   $179.95   $180.00  
  Purchase #4 $37.34   11.767%   $41.7338   $41.73   $41.75   $41.70  
  Purchase #5 $190.75   8.746%   $207.433   $207.43   $207.45   $207.40  
  Purchase #6 $197.88   8.365%   $214.4327   $214.43   $214.45   $214.40  
  Purchase #7 $250.81   11.193%   $278.8832   $278.88   $278.90   $278.90  
  7 purchase totals = $983.73       $1,069.3738   $1,069.36   $1,069.45   $1,069.30