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 $52.96   4.562%   $55.376   $55.38   $55.40   $55.40  
  Purchase #2 $212.52   3.706%   $220.396   $220.40   $220.40   $220.40  
  Purchase #3 $182.88   5.227%   $192.4391   $192.44   $192.45   $192.40  
  Purchase #4 $147.51   7.794%   $159.0069   $159.01   $159.00   $159.00  
  Purchase #5 $57.91   11.796%   $64.7411   $64.74   $64.75   $64.70  
  Purchase #6 $138.94   10.301%   $153.2522   $153.25   $153.25   $153.30  
  Purchase #7 $98.65   6.195%   $104.7614   $104.76   $104.75   $104.80  
  7 purchase totals = $891.37       $949.9727   $949.98   $950.00   $950.00