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 $209.76   8.279%   $227.126   $227.13   $227.15   $227.10  
  Purchase #2 $228.91   8.255%   $247.8065   $247.81   $247.80   $247.80  
  Purchase #3 $60.85   6.577%   $64.8521   $64.85   $64.85   $64.90  
  Purchase #4 $170.56   12.319%   $191.5713   $191.57   $191.55   $191.60  
  Purchase #5 $177.88   5.839%   $188.2664   $188.27   $188.25   $188.30  
  Purchase #6 $207.25   6.592%   $220.9119   $220.91   $220.90   $220.90  
  Purchase #7 $19.98   10.196%   $22.0172   $22.02   $22.00   $22.00  
  7 purchase totals = $1,075.19       $1,162.5514   $1,162.56   $1,162.50   $1,162.60