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 $157.56   10.169%   $173.5823   $173.58   $173.60   $173.60  
  Purchase #2 $60.71   7.245%   $65.1084   $65.11   $65.10   $65.10  
  Purchase #3 $86.62   10.270%   $95.5159   $95.52   $95.50   $95.50  
  Purchase #4 $241.34   3.851%   $250.634   $250.63   $250.65   $250.60  
  Purchase #5 $53.68   12.172%   $60.2139   $60.21   $60.20   $60.20  
  Purchase #6 $115.77   12.819%   $130.6106   $130.61   $130.60   $130.60  
  Purchase #7 $77.88   6.307%   $82.7919   $82.79   $82.80   $82.80  
  7 purchase totals = $793.56       $858.4570   $858.45   $858.45   $858.40