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 $227.59   8.522%   $246.9852   $246.99   $247.00   $247.00  
  Purchase #2 $177.30   9.248%   $193.6967   $193.70   $193.70   $193.70  
  Purchase #3 $241.93   11.139%   $268.8786   $268.88   $268.90   $268.90  
  Purchase #4 $141.59   10.382%   $156.2899   $156.29   $156.30   $156.30  
  Purchase #5 $32.49   6.532%   $34.6122   $34.61   $34.60   $34.60  
  Purchase #6 $208.71   9.353%   $228.2306   $228.23   $228.25   $228.20  
  Purchase #7 $68.77   9.190%   $75.09   $75.09   $75.10   $75.10  
  7 purchase totals = $1,098.38       $1,203.7832   $1,203.79   $1,203.85   $1,203.80