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 $228.77   5.743%   $241.9083   $241.91   $241.90   $241.90  
  Purchase #2 $218.38   6.551%   $232.6861   $232.69   $232.70   $232.70  
  Purchase #3 $107.36   11.665%   $119.8835   $119.88   $119.90   $119.90  
  Purchase #4 $229.44   13.608%   $260.6622   $260.66   $260.65   $260.70  
  Purchase #5 $157.37   3.270%   $162.516   $162.52   $162.50   $162.50  
  Purchase #6 $35.31   8.352%   $38.2591   $38.26   $38.25   $38.30  
  Purchase #7 $109.90   12.816%   $123.9848   $123.98   $124.00   $124.00  
  7 purchase totals = $1,086.53       $1,179.9000   $1,179.90   $1,179.90   $1,180.00