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 $243.93   4.231%   $254.2507   $254.25   $254.25   $254.30  
  Purchase #2 $164.88   12.737%   $185.8808   $185.88   $185.90   $185.90  
  Purchase #3 $88.61   10.212%   $97.6589   $97.66   $97.65   $97.70  
  Purchase #4 $220.56   3.156%   $227.5209   $227.52   $227.50   $227.50  
  Purchase #5 $96.93   6.835%   $103.5552   $103.56   $103.55   $103.60  
  Purchase #6 $207.62   13.364%   $235.3663   $235.37   $235.35   $235.40  
  Purchase #7 $12.40   12.713%   $13.9764   $13.98   $14.00   $14.00  
  7 purchase totals = $1,034.93       $1,118.2092   $1,118.22   $1,118.20   $1,118.40