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 $176.79   10.704%   $195.7136   $195.71   $195.70   $195.70  
  Purchase #2 $60.41   7.762%   $65.099   $65.10   $65.10   $65.10  
  Purchase #3 $53.62   8.836%   $58.3579   $58.36   $58.35   $58.40  
  Purchase #4 $238.62   5.808%   $252.479   $252.48   $252.50   $252.50  
  Purchase #5 $99.81   3.102%   $102.9061   $102.91   $102.90   $102.90  
  Purchase #6 $185.52   11.691%   $207.2091   $207.21   $207.20   $207.20  
  Purchase #7 $45.95   12.139%   $51.5279   $51.53   $51.55   $51.50  
  7 purchase totals = $860.72       $933.2926   $933.30   $933.30   $933.30