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 $216.93   8.819%   $236.0611   $236.06   $236.05   $236.10  
  Purchase #2 $24.46   10.255%   $26.9684   $26.97   $26.95   $27.00  
  Purchase #3 $230.39   4.397%   $240.5202   $240.52   $240.50   $240.50  
  Purchase #4 $108.65   12.693%   $122.4409   $122.44   $122.45   $122.40  
  Purchase #5 $228.65   3.116%   $235.7747   $235.77   $235.75   $235.80  
  Purchase #6 $236.65   12.111%   $265.3107   $265.31   $265.30   $265.30  
  Purchase #7 $187.64   4.758%   $196.5679   $196.57   $196.55   $196.60  
  7 purchase totals = $1,233.37       $1,323.6439   $1,323.64   $1,323.55   $1,323.70