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 $185.60   11.791%   $207.4841   $207.48   $207.50   $207.50  
  Purchase #2 $152.52   5.503%   $160.9132   $160.91   $160.90   $160.90  
  Purchase #3 $73.55   12.401%   $82.6709   $82.67   $82.65   $82.70  
  Purchase #4 $245.94   3.155%   $253.6994   $253.70   $253.70   $253.70  
  Purchase #5 $237.95   4.403%   $248.4269   $248.43   $248.45   $248.40  
  Purchase #6 $61.69   9.634%   $67.6332   $67.63   $67.65   $67.60  
  Purchase #7 $247.84   11.550%   $276.4655   $276.47   $276.45   $276.50  
  7 purchase totals = $1,205.09       $1,297.2932   $1,297.29   $1,297.30   $1,297.30