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 $202.65   11.156%   $225.2576   $225.26   $225.25   $225.30  
  Purchase #2 $143.48   5.246%   $151.007   $151.01   $151.00   $151.00  
  Purchase #3 $103.71   7.504%   $111.4924   $111.49   $111.50   $111.50  
  Purchase #4 $221.93   5.366%   $233.8388   $233.84   $233.85   $233.80  
  Purchase #5 $154.36   13.339%   $174.9501   $174.95   $174.95   $175.00  
  Purchase #6 $135.80   13.765%   $154.4929   $154.49   $154.50   $154.50  
  Purchase #7 $79.49   9.243%   $86.8373   $86.84   $86.85   $86.80  
  7 purchase totals = $1,041.42       $1,137.8761   $1,137.88   $1,137.90   $1,137.90