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 $168.58   8.656%   $183.1723   $183.17   $183.15   $183.20  
  Purchase #2 $33.79   3.640%   $35.02   $35.02   $35.00   $35.00  
  Purchase #3 $169.63   7.812%   $182.8815   $182.88   $182.90   $182.90  
  Purchase #4 $172.77   13.635%   $196.3272   $196.33   $196.35   $196.30  
  Purchase #5 $228.96   8.436%   $248.2751   $248.28   $248.30   $248.30  
  Purchase #6 $115.92   4.340%   $120.9509   $120.95   $120.95   $121.00  
  Purchase #7 $160.29   11.682%   $179.0151   $179.02   $179.00   $179.00  
  7 purchase totals = $1,049.94       $1,145.6421   $1,145.65   $1,145.65   $1,145.70