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 $235.83   13.490%   $267.6435   $267.64   $267.65   $267.60  
  Purchase #2 $196.36   11.683%   $219.3007   $219.30   $219.30   $219.30  
  Purchase #3 $8.72   9.848%   $9.5787   $9.58   $9.60   $9.60  
  Purchase #4 $208.62   13.838%   $237.4888   $237.49   $237.50   $237.50  
  Purchase #5 $221.89   6.432%   $236.162   $236.16   $236.15   $236.20  
  Purchase #6 $39.25   7.674%   $42.262   $42.26   $42.25   $42.30  
  Purchase #7 $22.41   7.170%   $24.0168   $24.02   $24.00   $24.00  
  7 purchase totals = $933.08       $1,036.4525   $1,036.45   $1,036.45   $1,036.50