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 $104.74   11.332%   $116.6091   $116.61   $116.60   $116.60  
  Purchase #2 $61.87   5.119%   $65.0371   $65.04   $65.05   $65.00  
  Purchase #3 $106.69   8.847%   $116.1289   $116.13   $116.15   $116.10  
  Purchase #4 $202.54   12.690%   $228.2423   $228.24   $228.25   $228.20  
  Purchase #5 $209.83   5.129%   $220.5922   $220.59   $220.60   $220.60  
  Purchase #6 $182.87   11.175%   $203.3057   $203.31   $203.30   $203.30  
  Purchase #7 $238.45   9.477%   $261.0479   $261.05   $261.05   $261.00  
  7 purchase totals = $1,106.99       $1,210.9632   $1,210.97   $1,211.00   $1,210.80