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 $102.64   10.671%   $113.5927   $113.59   $113.60   $113.60  
  Purchase #2 $107.58   10.820%   $119.2202   $119.22   $119.20   $119.20  
  Purchase #3 $72.58   11.301%   $80.7823   $80.78   $80.80   $80.80  
  Purchase #4 $245.67   3.792%   $254.9858   $254.99   $255.00   $255.00  
  Purchase #5 $138.51   11.296%   $154.1561   $154.16   $154.15   $154.20  
  Purchase #6 $85.96   13.360%   $97.4443   $97.44   $97.45   $97.40  
  Purchase #7 $240.28   3.357%   $248.3462   $248.35   $248.35   $248.30  
  7 purchase totals = $993.22       $1,068.5276   $1,068.53   $1,068.55   $1,068.50