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 $223.54   10.618%   $247.2755   $247.28   $247.30   $247.30  
  Purchase #2 $61.46   3.469%   $63.592   $63.59   $63.60   $63.60  
  Purchase #3 $92.82   3.142%   $95.7364   $95.74   $95.75   $95.70  
  Purchase #4 $163.83   6.594%   $174.633   $174.63   $174.65   $174.60  
  Purchase #5 $29.97   9.491%   $32.8145   $32.81   $32.80   $32.80  
  Purchase #6 $185.29   13.274%   $209.8854   $209.89   $209.90   $209.90  
  Purchase #7 $217.52   8.212%   $235.3827   $235.38   $235.40   $235.40  
  7 purchase totals = $974.43       $1,059.3195   $1,059.32   $1,059.40   $1,059.30