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 $52.99   8.654%   $57.5758   $57.58   $57.60   $57.60  
  Purchase #2 $175.60   13.510%   $199.3236   $199.32   $199.30   $199.30  
  Purchase #3 $75.37   13.305%   $85.398   $85.40   $85.40   $85.40  
  Purchase #4 $218.47   4.835%   $229.033   $229.03   $229.05   $229.00  
  Purchase #5 $29.95   9.234%   $32.7156   $32.72   $32.70   $32.70  
  Purchase #6 $12.39   8.631%   $13.4594   $13.46   $13.45   $13.50  
  Purchase #7 $219.71   12.416%   $246.9892   $246.99   $247.00   $247.00  
  7 purchase totals = $784.48       $864.4946   $864.50   $864.50   $864.50