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 $34.61   8.465%   $37.5397   $37.54   $37.55   $37.50  
  Purchase #2 $163.87   8.583%   $177.935   $177.94   $177.95   $177.90  
  Purchase #3 $127.90   10.495%   $141.3231   $141.32   $141.30   $141.30  
  Purchase #4 $228.44   8.590%   $248.063   $248.06   $248.05   $248.10  
  Purchase #5 $41.30   5.126%   $43.417   $43.42   $43.40   $43.40  
  Purchase #6 $124.91   5.258%   $131.4778   $131.48   $131.50   $131.50  
  Purchase #7 $58.64   5.783%   $62.0312   $62.03   $62.05   $62.00  
  7 purchase totals = $779.67       $841.7868   $841.79   $841.80   $841.70