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 $59.93   5.670%   $63.328   $63.33   $63.35   $63.30  
  Purchase #2 $127.43   5.726%   $134.7266   $134.73   $134.75   $134.70  
  Purchase #3 $216.38   10.211%   $238.4746   $238.47   $238.45   $238.50  
  Purchase #4 $187.40   3.861%   $194.6355   $194.64   $194.65   $194.60  
  Purchase #5 $232.83   9.431%   $254.7882   $254.79   $254.80   $254.80  
  Purchase #6 $62.27   5.741%   $65.8449   $65.84   $65.85   $65.80  
  Purchase #7 $43.84   7.848%   $47.2806   $47.28   $47.30   $47.30  
  7 purchase totals = $930.08       $999.0784   $999.08   $999.15   $999.00