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 $206.27   9.239%   $225.3273   $225.33   $225.35   $225.30  
  Purchase #2 $38.67   7.703%   $41.6488   $41.65   $41.65   $41.60  
  Purchase #3 $68.26   13.626%   $77.5611   $77.56   $77.55   $77.60  
  Purchase #4 $114.94   3.613%   $119.0928   $119.09   $119.10   $119.10  
  Purchase #5 $102.84   4.251%   $107.2117   $107.21   $107.20   $107.20  
  Purchase #6 $101.69   9.326%   $111.1736   $111.17   $111.15   $111.20  
  Purchase #7 $243.54   10.666%   $269.516   $269.52   $269.50   $269.50  
  7 purchase totals = $876.21       $951.5313   $951.53   $951.50   $951.50