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 $53.54   6.297%   $56.9114   $56.91   $56.90   $56.90  
  Purchase #2 $136.46   8.206%   $147.6579   $147.66   $147.65   $147.70  
  Purchase #3 $213.49   10.323%   $235.5286   $235.53   $235.55   $235.50  
  Purchase #4 $80.89   11.617%   $90.287   $90.29   $90.30   $90.30  
  Purchase #5 $64.35   7.353%   $69.0817   $69.08   $69.10   $69.10  
  Purchase #6 $247.61   7.481%   $266.1337   $266.13   $266.15   $266.10  
  Purchase #7 $202.47   12.159%   $227.0883   $227.09   $227.10   $227.10  
  7 purchase totals = $998.81       $1,092.6886   $1,092.69   $1,092.75   $1,092.70