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 $192.69   12.463%   $216.705   $216.71   $216.70   $216.70  
  Purchase #2 $221.92   6.248%   $235.7856   $235.79   $235.80   $235.80  
  Purchase #3 $72.58   7.460%   $77.9945   $77.99   $78.00   $78.00  
  Purchase #4 $81.51   6.173%   $86.5416   $86.54   $86.55   $86.50  
  Purchase #5 $54.99   9.461%   $60.1926   $60.19   $60.20   $60.20  
  Purchase #6 $168.45   10.598%   $186.3023   $186.30   $186.30   $186.30  
  Purchase #7 $43.26   9.861%   $47.5259   $47.53   $47.55   $47.50  
  7 purchase totals = $835.40       $911.0475   $911.05   $911.10   $911.00