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 $226.25   11.561%   $252.4068   $252.41   $252.40   $252.40  
  Purchase #2 $116.97   11.289%   $130.1747   $130.17   $130.15   $130.20  
  Purchase #3 $164.58   13.584%   $186.9365   $186.94   $186.95   $186.90  
  Purchase #4 $27.51   11.153%   $30.5782   $30.58   $30.60   $30.60  
  Purchase #5 $179.80   8.362%   $194.8349   $194.83   $194.85   $194.80  
  Purchase #6 $194.67   13.190%   $220.347   $220.35   $220.35   $220.30  
  Purchase #7 $85.37   7.713%   $91.9546   $91.95   $91.95   $92.00  
  7 purchase totals = $995.15       $1,107.2327   $1,107.23   $1,107.25   $1,107.20