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 $192.82   11.649%   $215.2816   $215.28   $215.30   $215.30  
  Purchase #2 $104.46   10.365%   $115.2873   $115.29   $115.30   $115.30  
  Purchase #3 $14.92   11.718%   $16.6683   $16.67   $16.65   $16.70  
  Purchase #4 $235.95   9.576%   $258.5446   $258.54   $258.55   $258.50  
  Purchase #5 $162.39   12.113%   $182.0603   $182.06   $182.05   $182.10  
  Purchase #6 $216.91   7.341%   $232.8334   $232.83   $232.85   $232.80  
  Purchase #7 $71.57   13.212%   $81.0258   $81.03   $81.05   $81.00  
  7 purchase totals = $999.02       $1,101.7013   $1,101.70   $1,101.75   $1,101.70