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 $90.64   5.312%   $95.4548   $95.45   $95.45   $95.50  
  Purchase #2 $185.89   8.242%   $201.2111   $201.21   $201.20   $201.20  
  Purchase #3 $29.53   10.464%   $32.62   $32.62   $32.60   $32.60  
  Purchase #4 $89.91   8.558%   $97.6045   $97.60   $97.60   $97.60  
  Purchase #5 $109.53   7.538%   $117.7864   $117.79   $117.80   $117.80  
  Purchase #6 $148.75   6.248%   $158.0439   $158.04   $158.05   $158.00  
  Purchase #7 $179.35   12.579%   $201.9104   $201.91   $201.90   $201.90  
  7 purchase totals = $833.60       $904.6311   $904.62   $904.60   $904.60