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 $208.49   8.613%   $226.4472   $226.45   $226.45   $226.40  
  Purchase #2 $178.55   8.451%   $193.6393   $193.64   $193.65   $193.60  
  Purchase #3 $168.85   7.647%   $181.762   $181.76   $181.75   $181.80  
  Purchase #4 $182.71   3.679%   $189.4319   $189.43   $189.45   $189.40  
  Purchase #5 $119.78   3.147%   $123.5495   $123.55   $123.55   $123.50  
  Purchase #6 $17.93   4.849%   $18.7994   $18.80   $18.80   $18.80  
  Purchase #7 $118.90   5.372%   $125.2873   $125.29   $125.30   $125.30  
  7 purchase totals = $995.21       $1,058.9166   $1,058.92   $1,058.95   $1,058.80