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 $57.51   13.549%   $65.302   $65.30   $65.30   $65.30  
  Purchase #2 $61.63   8.591%   $66.9246   $66.92   $66.90   $66.90  
  Purchase #3 $117.56   4.597%   $122.9642   $122.96   $122.95   $123.00  
  Purchase #4 $113.41   11.506%   $126.459   $126.46   $126.45   $126.50  
  Purchase #5 $216.84   10.684%   $240.0072   $240.01   $240.00   $240.00  
  Purchase #6 $180.88   6.650%   $192.9085   $192.91   $192.90   $192.90  
  Purchase #7 $37.80   3.251%   $39.0289   $39.03   $39.05   $39.00  
  7 purchase totals = $785.63       $853.5944   $853.59   $853.55   $853.60