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 $201.46   8.436%   $218.4552   $218.46   $218.45   $218.50  
  Purchase #2 $120.72   8.258%   $130.6891   $130.69   $130.70   $130.70  
  Purchase #3 $182.54   8.839%   $198.6747   $198.67   $198.65   $198.70  
  Purchase #4 $169.86   7.193%   $182.078   $182.08   $182.10   $182.10  
  Purchase #5 $209.92   11.406%   $233.8635   $233.86   $233.85   $233.90  
  Purchase #6 $157.96   9.675%   $173.2426   $173.24   $173.25   $173.20  
  Purchase #7 $213.36   8.174%   $230.8   $230.80   $230.80   $230.80  
  7 purchase totals = $1,255.82       $1,367.8031   $1,367.80   $1,367.80   $1,367.90