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 $243.57   13.615%   $276.7321   $276.73   $276.75   $276.70  
  Purchase #2 $59.84   12.483%   $67.3098   $67.31   $67.30   $67.30  
  Purchase #3 $125.59   5.219%   $132.1445   $132.14   $132.15   $132.10  
  Purchase #4 $209.48   11.273%   $233.0947   $233.09   $233.10   $233.10  
  Purchase #5 $217.70   6.688%   $232.2598   $232.26   $232.25   $232.30  
  Purchase #6 $88.71   4.118%   $92.3631   $92.36   $92.35   $92.40  
  Purchase #7 $119.59   13.343%   $135.5469   $135.55   $135.55   $135.50  
  7 purchase totals = $1,064.48       $1,169.4509   $1,169.44   $1,169.45   $1,169.40