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 $219.43   8.622%   $238.3493   $238.35   $238.35   $238.30  
  Purchase #2 $62.86   3.761%   $65.2242   $65.22   $65.20   $65.20  
  Purchase #3 $39.55   7.310%   $42.4411   $42.44   $42.45   $42.40  
  Purchase #4 $214.25   5.579%   $226.203   $226.20   $226.20   $226.20  
  Purchase #5 $243.40   13.661%   $276.6509   $276.65   $276.65   $276.70  
  Purchase #6 $237.56   4.569%   $248.4141   $248.41   $248.40   $248.40  
  Purchase #7 $170.75   6.711%   $182.209   $182.21   $182.20   $182.20  
  7 purchase totals = $1,187.80       $1,279.4916   $1,279.48   $1,279.45   $1,279.40