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 $66.76   10.122%   $73.5174   $73.52   $73.50   $73.50  
  Purchase #2 $208.76   13.136%   $236.1827   $236.18   $236.20   $236.20  
  Purchase #3 $235.62   11.212%   $262.0377   $262.04   $262.05   $262.00  
  Purchase #4 $45.88   7.483%   $49.3132   $49.31   $49.30   $49.30  
  Purchase #5 $245.57   4.279%   $256.0779   $256.08   $256.10   $256.10  
  Purchase #6 $236.99   8.832%   $257.921   $257.92   $257.90   $257.90  
  Purchase #7 $215.86   7.119%   $231.2271   $231.23   $231.25   $231.20  
  7 purchase totals = $1,255.44       $1,366.2770   $1,366.28   $1,366.30   $1,366.20