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 $106.41   11.464%   $118.6088   $118.61   $118.60   $118.60  
  Purchase #2 $140.95   12.541%   $158.6265   $158.63   $158.65   $158.60  
  Purchase #3 $30.59   8.432%   $33.1693   $33.17   $33.15   $33.20  
  Purchase #4 $70.99   4.323%   $74.0589   $74.06   $74.05   $74.10  
  Purchase #5 $109.28   13.596%   $124.1377   $124.14   $124.15   $124.10  
  Purchase #6 $204.40   9.114%   $223.029   $223.03   $223.05   $223.00  
  Purchase #7 $236.94   12.510%   $266.5812   $266.58   $266.60   $266.60  
  7 purchase totals = $899.56       $998.2114   $998.22   $998.25   $998.20