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 $243.95   5.860%   $258.2455   $258.25   $258.25   $258.20  
  Purchase #2 $220.58   3.111%   $227.4422   $227.44   $227.45   $227.40  
  Purchase #3 $165.28   8.565%   $179.4362   $179.44   $179.45   $179.40  
  Purchase #4 $121.85   10.625%   $134.7966   $134.80   $134.80   $134.80  
  Purchase #5 $206.99   10.627%   $228.9868   $228.99   $229.00   $229.00  
  Purchase #6 $31.95   11.734%   $35.699   $35.70   $35.70   $35.70  
  Purchase #7 $80.91   11.554%   $90.2583   $90.26   $90.25   $90.30  
  7 purchase totals = $1,071.51       $1,154.8646   $1,154.88   $1,154.90   $1,154.80