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 $61.91   11.703%   $69.1553   $69.16   $69.15   $69.20  
  Purchase #2 $84.39   4.643%   $88.3082   $88.31   $88.30   $88.30  
  Purchase #3 $111.62   11.867%   $124.8659   $124.87   $124.85   $124.90  
  Purchase #4 $63.81   8.152%   $69.0118   $69.01   $69.00   $69.00  
  Purchase #5 $86.40   8.666%   $93.8874   $93.89   $93.90   $93.90  
  Purchase #6 $228.34   11.714%   $255.0877   $255.09   $255.10   $255.10  
  Purchase #7 $63.72   4.582%   $66.6397   $66.64   $66.65   $66.60  
  7 purchase totals = $700.19       $766.9560   $766.97   $766.95   $767.00