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 $90.33   10.176%   $99.522   $99.52   $99.50   $99.50  
  Purchase #2 $192.30   5.457%   $202.7938   $202.79   $202.80   $202.80  
  Purchase #3 $90.53   6.141%   $96.0894   $96.09   $96.10   $96.10  
  Purchase #4 $56.61   7.607%   $60.9163   $60.92   $60.90   $60.90  
  Purchase #5 $177.39   4.803%   $185.91   $185.91   $185.90   $185.90  
  Purchase #6 $142.54   8.566%   $154.75   $154.75   $154.75   $154.80  
  Purchase #7 $245.92   7.817%   $265.1436   $265.14   $265.15   $265.10  
  7 purchase totals = $995.62       $1,065.1251   $1,065.12   $1,065.10   $1,065.10