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 $24.93   8.309%   $27.0014   $27.00   $27.00   $27.00  
  Purchase #2 $228.56   3.542%   $236.6556   $236.66   $236.65   $236.70  
  Purchase #3 $204.53   13.461%   $232.0618   $232.06   $232.05   $232.10  
  Purchase #4 $96.88   6.122%   $102.811   $102.81   $102.80   $102.80  
  Purchase #5 $192.40   5.462%   $202.9089   $202.91   $202.90   $202.90  
  Purchase #6 $177.69   4.482%   $185.6541   $185.65   $185.65   $185.70  
  Purchase #7 $87.57   13.130%   $99.0679   $99.07   $99.05   $99.10  
  7 purchase totals = $1,012.56       $1,086.1607   $1,086.16   $1,086.10   $1,086.30