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 $217.27   8.207%   $235.1013   $235.10   $235.10   $235.10  
  Purchase #2 $114.41   3.353%   $118.2462   $118.25   $118.25   $118.20  
  Purchase #3 $155.95   7.121%   $167.0552   $167.06   $167.05   $167.10  
  Purchase #4 $72.95   6.295%   $77.5422   $77.54   $77.55   $77.50  
  Purchase #5 $175.61   3.791%   $182.2674   $182.27   $182.25   $182.30  
  Purchase #6 $223.76   5.655%   $236.4136   $236.41   $236.40   $236.40  
  Purchase #7 $28.55   9.677%   $31.3128   $31.31   $31.30   $31.30  
  7 purchase totals = $988.50       $1,047.9387   $1,047.94   $1,047.90   $1,047.90