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 $68.92   10.715%   $76.3048   $76.30   $76.30   $76.30  
  Purchase #2 $180.96   8.437%   $196.2276   $196.23   $196.25   $196.20  
  Purchase #3 $110.90   10.572%   $122.6243   $122.62   $122.60   $122.60  
  Purchase #4 $61.74   6.853%   $65.971   $65.97   $65.95   $66.00  
  Purchase #5 $232.56   11.362%   $258.9835   $258.98   $259.00   $259.00  
  Purchase #6 $24.88   8.595%   $27.0184   $27.02   $27.00   $27.00  
  Purchase #7 $12.67   10.224%   $13.9654   $13.97   $13.95   $14.00  
  7 purchase totals = $692.63       $761.0950   $761.09   $761.05   $761.10