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 $208.39   7.136%   $223.2607   $223.26   $223.25   $223.30  
  Purchase #2 $194.30   4.302%   $202.6588   $202.66   $202.65   $202.70  
  Purchase #3 $73.95   13.270%   $83.7632   $83.76   $83.75   $83.80  
  Purchase #4 $116.42   10.580%   $128.7372   $128.74   $128.75   $128.70  
  Purchase #5 $222.47   6.790%   $237.5757   $237.58   $237.60   $237.60  
  Purchase #6 $140.44   3.103%   $144.7979   $144.80   $144.80   $144.80  
  Purchase #7 $181.45   3.261%   $187.3671   $187.37   $187.35   $187.40  
  7 purchase totals = $1,137.42       $1,208.1606   $1,208.17   $1,208.15   $1,208.30