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 $126.32   11.668%   $141.059   $141.06   $141.05   $141.10  
  Purchase #2 $198.55   9.865%   $218.137   $218.14   $218.15   $218.10  
  Purchase #3 $39.78   11.172%   $44.2242   $44.22   $44.20   $44.20  
  Purchase #4 $208.44   13.104%   $235.754   $235.75   $235.75   $235.80  
  Purchase #5 $48.99   6.824%   $52.3331   $52.33   $52.35   $52.30  
  Purchase #6 $208.49   8.871%   $226.9851   $226.99   $227.00   $227.00  
  Purchase #7 $139.48   13.664%   $158.5385   $158.54   $158.55   $158.50  
  7 purchase totals = $970.05       $1,077.0309   $1,077.03   $1,077.05   $1,077.00