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 $210.95   11.397%   $234.992   $234.99   $235.00   $235.00  
  Purchase #2 $82.81   13.137%   $93.6887   $93.69   $93.70   $93.70  
  Purchase #3 $61.99   4.342%   $64.6816   $64.68   $64.70   $64.70  
  Purchase #4 $151.97   11.163%   $168.9344   $168.93   $168.95   $168.90  
  Purchase #5 $161.89   9.348%   $177.0235   $177.02   $177.00   $177.00  
  Purchase #6 $153.55   11.122%   $170.6278   $170.63   $170.65   $170.60  
  Purchase #7 $5.99   9.867%   $6.581   $6.58   $6.60   $6.60  
  7 purchase totals = $829.15       $916.5290   $916.52   $916.60   $916.50