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 $33.54   13.280%   $37.9941   $37.99   $38.00   $38.00  
  Purchase #2 $211.71   7.691%   $227.9926   $227.99   $228.00   $228.00  
  Purchase #3 $152.26   6.185%   $161.6773   $161.68   $161.70   $161.70  
  Purchase #4 $222.99   5.493%   $235.2388   $235.24   $235.25   $235.20  
  Purchase #5 $119.91   7.775%   $129.233   $129.23   $129.25   $129.20  
  Purchase #6 $172.50   8.655%   $187.4299   $187.43   $187.45   $187.40  
  Purchase #7 $60.76   13.568%   $69.0039   $69.00   $69.00   $69.00  
  7 purchase totals = $973.67       $1,048.5696   $1,048.56   $1,048.65   $1,048.50