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 $233.47   12.646%   $262.9946   $262.99   $263.00   $263.00  
  Purchase #2 $120.90   9.798%   $132.7458   $132.75   $132.75   $132.70  
  Purchase #3 $134.30   9.762%   $147.4104   $147.41   $147.40   $147.40  
  Purchase #4 $151.94   6.239%   $161.4195   $161.42   $161.40   $161.40  
  Purchase #5 $156.72   6.767%   $167.3252   $167.33   $167.35   $167.30  
  Purchase #6 $112.93   11.874%   $126.3393   $126.34   $126.35   $126.30  
  Purchase #7 $46.89   8.182%   $50.7265   $50.73   $50.75   $50.70  
  7 purchase totals = $957.15       $1,048.9613   $1,048.97   $1,049.00   $1,048.80