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 $94.63   3.777%   $98.2042   $98.20   $98.20   $98.20  
  Purchase #2 $183.97   5.133%   $193.4132   $193.41   $193.40   $193.40  
  Purchase #3 $97.39   11.739%   $108.8226   $108.82   $108.80   $108.80  
  Purchase #4 $211.54   11.652%   $236.1886   $236.19   $236.20   $236.20  
  Purchase #5 $86.43   3.270%   $89.2563   $89.26   $89.25   $89.30  
  Purchase #6 $177.68   11.751%   $198.5592   $198.56   $198.55   $198.60  
  Purchase #7 $85.86   5.739%   $90.7875   $90.79   $90.80   $90.80  
  7 purchase totals = $937.50       $1,015.2316   $1,015.23   $1,015.20   $1,015.30