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 $114.79   11.118%   $127.5524   $127.55   $127.55   $127.60  
  Purchase #2 $187.62   7.135%   $201.0067   $201.01   $201.00   $201.00  
  Purchase #3 $62.77   12.281%   $70.4788   $70.48   $70.50   $70.50  
  Purchase #4 $183.47   8.138%   $198.4008   $198.40   $198.40   $198.40  
  Purchase #5 $208.96   13.576%   $237.3284   $237.33   $237.35   $237.30  
  Purchase #6 $150.95   3.287%   $155.9117   $155.91   $155.90   $155.90  
  Purchase #7 $13.27   11.363%   $14.7779   $14.78   $14.80   $14.80  
  7 purchase totals = $921.83       $1,005.4567   $1,005.46   $1,005.50   $1,005.50