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 $177.57   6.393%   $188.9221   $188.92   $188.90   $188.90  
  Purchase #2 $68.77   11.501%   $76.6792   $76.68   $76.70   $76.70  
  Purchase #3 $50.83   11.810%   $56.833   $56.83   $56.85   $56.80  
  Purchase #4 $201.58   12.719%   $227.219   $227.22   $227.20   $227.20  
  Purchase #5 $147.91   6.124%   $156.968   $156.97   $156.95   $157.00  
  Purchase #6 $88.71   8.462%   $96.2166   $96.22   $96.20   $96.20  
  Purchase #7 $240.26   7.449%   $258.157   $258.16   $258.15   $258.20  
  7 purchase totals = $975.63       $1,060.9949   $1,061.00   $1,060.95   $1,061.00