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 $89.69   8.847%   $97.6249   $97.62   $97.60   $97.60  
  Purchase #2 $71.85   5.442%   $75.7601   $75.76   $75.75   $75.80  
  Purchase #3 $218.82   3.393%   $226.2446   $226.24   $226.25   $226.20  
  Purchase #4 $208.47   6.545%   $222.1144   $222.11   $222.10   $222.10  
  Purchase #5 $85.81   11.240%   $95.455   $95.46   $95.45   $95.50  
  Purchase #6 $169.64   7.118%   $181.715   $181.72   $181.70   $181.70  
  Purchase #7 $11.98   3.255%   $12.3699   $12.37   $12.35   $12.40  
  7 purchase totals = $856.26       $911.2839   $911.28   $911.20   $911.30