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 $207.39   9.258%   $226.5902   $226.59   $226.60   $226.60  
  Purchase #2 $162.87   11.578%   $181.7271   $181.73   $181.75   $181.70  
  Purchase #3 $162.77   8.244%   $176.1888   $176.19   $176.20   $176.20  
  Purchase #4 $246.99   4.717%   $258.6405   $258.64   $258.65   $258.60  
  Purchase #5 $152.35   3.654%   $157.9169   $157.92   $157.90   $157.90  
  Purchase #6 $9.79   13.693%   $11.1305   $11.13   $11.15   $11.10  
  Purchase #7 $144.31   10.863%   $159.9864   $159.99   $160.00   $160.00  
  7 purchase totals = $1,086.47       $1,172.1804   $1,172.19   $1,172.25   $1,172.10