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 $61.45   12.342%   $69.0342   $69.03   $69.05   $69.00  
  Purchase #2 $90.91   7.743%   $97.9492   $97.95   $97.95   $97.90  
  Purchase #3 $83.44   13.777%   $94.9355   $94.94   $94.95   $94.90  
  Purchase #4 $226.92   5.722%   $239.9044   $239.90   $239.90   $239.90  
  Purchase #5 $207.40   7.294%   $222.5278   $222.53   $222.55   $222.50  
  Purchase #6 $69.82   11.694%   $77.9848   $77.98   $78.00   $78.00  
  Purchase #7 $246.29   4.490%   $257.3484   $257.35   $257.35   $257.30  
  7 purchase totals = $986.23       $1,059.6843   $1,059.68   $1,059.75   $1,059.50