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 $60.47   8.874%   $65.8361   $65.84   $65.85   $65.80  
  Purchase #2 $134.69   9.411%   $147.3657   $147.37   $147.35   $147.40  
  Purchase #3 $96.56   12.573%   $108.7005   $108.70   $108.70   $108.70  
  Purchase #4 $231.43   9.702%   $253.8833   $253.88   $253.90   $253.90  
  Purchase #5 $193.30   4.834%   $202.6441   $202.64   $202.65   $202.60  
  Purchase #6 $36.60   9.530%   $40.088   $40.09   $40.10   $40.10  
  Purchase #7 $65.58   11.688%   $73.245   $73.25   $73.25   $73.20  
  7 purchase totals = $818.63       $891.7627   $891.77   $891.80   $891.70