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 $92.50   6.456%   $98.4718   $98.47   $98.45   $98.50  
  Purchase #2 $199.70   5.839%   $211.3605   $211.36   $211.35   $211.40  
  Purchase #3 $63.51   11.775%   $70.9883   $70.99   $71.00   $71.00  
  Purchase #4 $97.56   10.612%   $107.9131   $107.91   $107.90   $107.90  
  Purchase #5 $142.67   6.464%   $151.8922   $151.89   $151.90   $151.90  
  Purchase #6 $76.72   6.114%   $81.4107   $81.41   $81.40   $81.40  
  Purchase #7 $213.81   3.783%   $221.8984   $221.90   $221.90   $221.90  
  7 purchase totals = $886.47       $943.9350   $943.93   $943.90   $944.00