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 $210.43   6.418%   $223.9354   $223.94   $223.95   $223.90  
  Purchase #2 $52.71   8.400%   $57.1376   $57.14   $57.15   $57.10  
  Purchase #3 $46.39   11.873%   $51.8979   $51.90   $51.90   $51.90  
  Purchase #4 $232.60   8.639%   $252.6943   $252.69   $252.70   $252.70  
  Purchase #5 $121.91   6.825%   $130.2304   $130.23   $130.25   $130.20  
  Purchase #6 $101.99   5.619%   $107.7208   $107.72   $107.70   $107.70  
  Purchase #7 $197.66   4.729%   $207.0073   $207.01   $207.00   $207.00  
  7 purchase totals = $963.69       $1,030.6237   $1,030.63   $1,030.65   $1,030.50