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 $203.86   10.874%   $226.0277   $226.03   $226.05   $226.00  
  Purchase #2 $130.42   13.142%   $147.5598   $147.56   $147.55   $147.60  
  Purchase #3 $114.93   13.688%   $130.6616   $130.66   $130.65   $130.70  
  Purchase #4 $71.68   12.149%   $80.3884   $80.39   $80.40   $80.40  
  Purchase #5 $76.41   12.580%   $86.0224   $86.02   $86.00   $86.00  
  Purchase #6 $180.49   10.825%   $200.028   $200.03   $200.05   $200.00  
  Purchase #7 $227.53   4.422%   $237.5914   $237.59   $237.60   $237.60  
  7 purchase totals = $1,005.32       $1,108.2793   $1,108.28   $1,108.30   $1,108.30