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 $242.93   8.116%   $262.6462   $262.65   $262.65   $262.60  
  Purchase #2 $55.72   13.214%   $63.0828   $63.08   $63.10   $63.10  
  Purchase #3 $87.88   10.848%   $97.4132   $97.41   $97.40   $97.40  
  Purchase #4 $41.73   8.762%   $45.3864   $45.39   $45.40   $45.40  
  Purchase #5 $244.48   10.205%   $269.4292   $269.43   $269.45   $269.40  
  Purchase #6 $56.45   9.641%   $61.8923   $61.89   $61.90   $61.90  
  Purchase #7 $68.69   10.299%   $75.7644   $75.76   $75.75   $75.80  
  7 purchase totals = $797.88       $875.6145   $875.61   $875.65   $875.60