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 $41.84   10.158%   $46.0901   $46.09   $46.10   $46.10  
  Purchase #2 $196.45   11.387%   $218.8198   $218.82   $218.80   $218.80  
  Purchase #3 $17.96   6.643%   $19.1531   $19.15   $19.15   $19.20  
  Purchase #4 $164.99   10.833%   $182.8634   $182.86   $182.85   $182.90  
  Purchase #5 $79.33   9.606%   $86.9504   $86.95   $86.95   $87.00  
  Purchase #6 $49.29   13.342%   $55.8663   $55.87   $55.85   $55.90  
  Purchase #7 $198.25   9.869%   $217.8153   $217.82   $217.80   $217.80  
  7 purchase totals = $748.11       $827.5584   $827.56   $827.50   $827.70