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 $69.46   10.821%   $76.9763   $76.98   $77.00   $77.00  
  Purchase #2 $238.72   4.842%   $250.2788   $250.28   $250.30   $250.30  
  Purchase #3 $67.55   4.508%   $70.5952   $70.60   $70.60   $70.60  
  Purchase #4 $168.94   10.621%   $186.8831   $186.88   $186.90   $186.90  
  Purchase #5 $34.29   5.183%   $36.0673   $36.07   $36.05   $36.10  
  Purchase #6 $165.90   8.164%   $179.4441   $179.44   $179.45   $179.40  
  Purchase #7 $81.33   5.769%   $86.0219   $86.02   $86.00   $86.00  
  7 purchase totals = $826.19       $886.2667   $886.27   $886.30   $886.30