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 $211.98   8.320%   $229.6167   $229.62   $229.60   $229.60  
  Purchase #2 $164.33   9.326%   $179.6554   $179.66   $179.65   $179.70  
  Purchase #3 $25.41   7.822%   $27.3976   $27.40   $27.40   $27.40  
  Purchase #4 $77.42   11.211%   $86.0996   $86.10   $86.10   $86.10  
  Purchase #5 $164.98   6.262%   $175.311   $175.31   $175.30   $175.30  
  Purchase #6 $25.76   4.815%   $27.0003   $27.00   $27.00   $27.00  
  Purchase #7 $225.40   6.607%   $240.2922   $240.29   $240.30   $240.30  
  7 purchase totals = $895.28       $965.3728   $965.38   $965.35   $965.40