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 $201.72   5.528%   $212.8711   $212.87   $212.85   $212.90  
  Purchase #2 $177.75   5.730%   $187.9351   $187.94   $187.95   $187.90  
  Purchase #3 $134.37   5.178%   $141.3277   $141.33   $141.35   $141.30  
  Purchase #4 $60.95   5.283%   $64.17   $64.17   $64.15   $64.20  
  Purchase #5 $31.99   3.383%   $33.0722   $33.07   $33.05   $33.10  
  Purchase #6 $198.61   8.737%   $215.9626   $215.96   $215.95   $216.00  
  Purchase #7 $127.79   9.759%   $140.261   $140.26   $140.25   $140.30  
  7 purchase totals = $933.18       $995.5997   $995.60   $995.55   $995.70