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 $212.83   12.323%   $239.057   $239.06   $239.05   $239.10  
  Purchase #2 $24.25   4.156%   $25.2578   $25.26   $25.25   $25.30  
  Purchase #3 $234.79   5.642%   $248.0369   $248.04   $248.05   $248.00  
  Purchase #4 $30.85   4.461%   $32.2262   $32.23   $32.25   $32.20  
  Purchase #5 $57.77   6.781%   $61.6874   $61.69   $61.70   $61.70  
  Purchase #6 $140.45   7.642%   $151.1832   $151.18   $151.20   $151.20  
  Purchase #7 $244.40   13.861%   $278.2763   $278.28   $278.30   $278.30  
  7 purchase totals = $945.34       $1,035.7248   $1,035.74   $1,035.80   $1,035.80