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 $116.38   9.243%   $127.137   $127.14   $127.15   $127.10  
  Purchase #2 $90.61   11.289%   $100.839   $100.84   $100.85   $100.80  
  Purchase #3 $206.76   13.339%   $234.3397   $234.34   $234.35   $234.30  
  Purchase #4 $44.80   11.279%   $49.853   $49.85   $49.85   $49.90  
  Purchase #5 $203.37   7.479%   $218.58   $218.58   $218.60   $218.60  
  Purchase #6 $26.87   11.752%   $30.0278   $30.03   $30.05   $30.00  
  Purchase #7 $31.92   9.869%   $35.0702   $35.07   $35.05   $35.10  
  7 purchase totals = $720.71       $795.8467   $795.85   $795.90   $795.80