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 $208.93   12.674%   $235.4098   $235.41   $235.40   $235.40  
  Purchase #2 $202.60   4.246%   $211.2024   $211.20   $211.20   $211.20  
  Purchase #3 $105.33   9.821%   $115.6745   $115.67   $115.65   $115.70  
  Purchase #4 $195.40   7.233%   $209.5333   $209.53   $209.55   $209.50  
  Purchase #5 $47.81   5.832%   $50.5983   $50.60   $50.60   $50.60  
  Purchase #6 $90.90   7.257%   $97.4966   $97.50   $97.50   $97.50  
  Purchase #7 $103.48   12.196%   $116.1004   $116.10   $116.10   $116.10  
  7 purchase totals = $954.45       $1,036.0153   $1,036.01   $1,036.00   $1,036.00