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 $112.59   6.186%   $119.5548   $119.55   $119.55   $119.60  
  Purchase #2 $225.51   4.324%   $235.2611   $235.26   $235.25   $235.30  
  Purchase #3 $215.71   5.694%   $227.9925   $227.99   $228.00   $228.00  
  Purchase #4 $53.83   10.804%   $59.6458   $59.65   $59.65   $59.60  
  Purchase #5 $87.94   11.246%   $97.8297   $97.83   $97.85   $97.80  
  Purchase #6 $107.92   5.736%   $114.1103   $114.11   $114.10   $114.10  
  Purchase #7 $27.44   13.193%   $31.0602   $31.06   $31.05   $31.10  
  7 purchase totals = $830.94       $885.4544   $885.45   $885.45   $885.50