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 $60.55   12.729%   $68.2574   $68.26   $68.25   $68.30  
  Purchase #2 $174.60   11.107%   $193.9928   $193.99   $194.00   $194.00  
  Purchase #3 $151.28   9.474%   $165.6123   $165.61   $165.60   $165.60  
  Purchase #4 $196.46   6.393%   $209.0197   $209.02   $209.00   $209.00  
  Purchase #5 $5.65   12.589%   $6.3613   $6.36   $6.35   $6.40  
  Purchase #6 $156.34   12.857%   $176.4406   $176.44   $176.45   $176.40  
  Purchase #7 $61.71   10.591%   $68.2457   $68.25   $68.25   $68.20  
  7 purchase totals = $806.59       $887.9298   $887.93   $887.90   $887.90