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 $169.80   7.773%   $182.9986   $183.00   $183.00   $183.00  
  Purchase #2 $176.77   7.643%   $190.2805   $190.28   $190.30   $190.30  
  Purchase #3 $197.65   11.344%   $220.0714   $220.07   $220.05   $220.10  
  Purchase #4 $80.27   6.448%   $85.4458   $85.45   $85.45   $85.40  
  Purchase #5 $45.76   13.224%   $51.8113   $51.81   $51.80   $51.80  
  Purchase #6 $71.58   3.367%   $73.9901   $73.99   $74.00   $74.00  
  Purchase #7 $198.33   5.822%   $209.8768   $209.88   $209.90   $209.90  
  7 purchase totals = $940.16       $1,014.4745   $1,014.48   $1,014.50   $1,014.50