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 $208.47   12.287%   $234.0847   $234.08   $234.10   $234.10  
  Purchase #2 $90.44   13.601%   $102.7407   $102.74   $102.75   $102.70  
  Purchase #3 $118.86   3.870%   $123.4599   $123.46   $123.45   $123.50  
  Purchase #4 $197.91   8.548%   $214.8273   $214.83   $214.85   $214.80  
  Purchase #5 $129.66   13.535%   $147.2095   $147.21   $147.20   $147.20  
  Purchase #6 $212.30   8.808%   $230.9994   $231.00   $231.00   $231.00  
  Purchase #7 $53.39   10.304%   $58.8913   $58.89   $58.90   $58.90  
  7 purchase totals = $1,011.03       $1,112.2128   $1,112.21   $1,112.25   $1,112.20