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 $202.62   4.387%   $211.5089   $211.51   $211.50   $211.50  
  Purchase #2 $93.45   10.433%   $103.1996   $103.20   $103.20   $103.20  
  Purchase #3 $143.45   7.235%   $153.8286   $153.83   $153.85   $153.80  
  Purchase #4 $13.92   3.393%   $14.3923   $14.39   $14.40   $14.40  
  Purchase #5 $165.41   6.326%   $175.8738   $175.87   $175.85   $175.90  
  Purchase #6 $182.71   5.350%   $192.485   $192.49   $192.50   $192.50  
  Purchase #7 $87.29   13.446%   $99.027   $99.03   $99.05   $99.00  
  7 purchase totals = $888.85       $950.3152   $950.32   $950.35   $950.30