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 $74.78   10.184%   $82.3956   $82.40   $82.40   $82.40  
  Purchase #2 $106.69   8.385%   $115.636   $115.64   $115.65   $115.60  
  Purchase #3 $219.57   11.725%   $245.3146   $245.31   $245.30   $245.30  
  Purchase #4 $127.77   7.224%   $137.0001   $137.00   $137.00   $137.00  
  Purchase #5 $169.32   5.850%   $179.2252   $179.23   $179.25   $179.20  
  Purchase #6 $50.36   13.196%   $57.0055   $57.01   $57.00   $57.00  
  Purchase #7 $247.54   7.743%   $266.707   $266.71   $266.70   $266.70  
  7 purchase totals = $996.03       $1,083.2840   $1,083.30   $1,083.30   $1,083.20