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 $182.59   13.685%   $207.5774   $207.58   $207.60   $207.60  
  Purchase #2 $106.81   8.770%   $116.1772   $116.18   $116.20   $116.20  
  Purchase #3 $76.52   12.579%   $86.1455   $86.15   $86.15   $86.10  
  Purchase #4 $30.68   8.656%   $33.3357   $33.34   $33.35   $33.30  
  Purchase #5 $226.76   10.251%   $250.0052   $250.01   $250.00   $250.00  
  Purchase #6 $89.82   13.362%   $101.8217   $101.82   $101.80   $101.80  
  Purchase #7 $186.71   6.785%   $199.3783   $199.38   $199.40   $199.40  
  7 purchase totals = $899.89       $994.4410   $994.46   $994.50   $994.40