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 $114.33   11.778%   $127.7958   $127.80   $127.80   $127.80  
  Purchase #2 $201.71   11.594%   $225.0963   $225.10   $225.10   $225.10  
  Purchase #3 $191.29   11.113%   $212.5481   $212.55   $212.55   $212.50  
  Purchase #4 $87.40   12.307%   $98.1563   $98.16   $98.15   $98.20  
  Purchase #5 $135.77   13.464%   $154.0501   $154.05   $154.05   $154.10  
  Purchase #6 $169.61   13.213%   $192.0206   $192.02   $192.00   $192.00  
  Purchase #7 $43.37   12.466%   $48.7765   $48.78   $48.80   $48.80  
  7 purchase totals = $943.48       $1,058.4437   $1,058.46   $1,058.45   $1,058.50