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 $222.63   13.353%   $252.3578   $252.36   $252.35   $252.40  
  Purchase #2 $64.52   9.522%   $70.6636   $70.66   $70.65   $70.70  
  Purchase #3 $54.77   3.126%   $56.4821   $56.48   $56.50   $56.50  
  Purchase #4 $196.55   6.471%   $209.2688   $209.27   $209.25   $209.30  
  Purchase #5 $152.49   9.747%   $167.3532   $167.35   $167.35   $167.40  
  Purchase #6 $144.54   8.727%   $157.154   $157.15   $157.15   $157.20  
  Purchase #7 $88.56   7.862%   $95.5226   $95.52   $95.50   $95.50  
  7 purchase totals = $924.06       $1,008.8021   $1,008.79   $1,008.75   $1,009.00