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 $209.27   11.592%   $233.5286   $233.53   $233.55   $233.50  
  Purchase #2 $54.58   10.585%   $60.3573   $60.36   $60.35   $60.40  
  Purchase #3 $66.55   10.103%   $73.2735   $73.27   $73.25   $73.30  
  Purchase #4 $227.33   5.647%   $240.1673   $240.17   $240.15   $240.20  
  Purchase #5 $235.75   10.545%   $260.6098   $260.61   $260.60   $260.60  
  Purchase #6 $38.62   5.263%   $40.6526   $40.65   $40.65   $40.70  
  Purchase #7 $99.99   4.694%   $104.6835   $104.68   $104.70   $104.70  
  7 purchase totals = $932.09       $1,013.2726   $1,013.27   $1,013.25   $1,013.40