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 $239.25   4.814%   $250.7675   $250.77   $250.75   $250.80  
  Purchase #2 $144.82   6.786%   $154.6475   $154.65   $154.65   $154.60  
  Purchase #3 $54.83   6.657%   $58.48   $58.48   $58.50   $58.50  
  Purchase #4 $194.40   5.134%   $204.3805   $204.38   $204.40   $204.40  
  Purchase #5 $195.72   9.619%   $214.5463   $214.55   $214.55   $214.50  
  Purchase #6 $37.80   12.479%   $42.5171   $42.52   $42.50   $42.50  
  Purchase #7 $214.88   10.589%   $237.6336   $237.63   $237.65   $237.60  
  7 purchase totals = $1,081.70       $1,162.9725   $1,162.98   $1,163.00   $1,162.90