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 $53.47   6.369%   $56.8755   $56.88   $56.90   $56.90  
  Purchase #2 $33.47   13.723%   $38.0631   $38.06   $38.05   $38.10  
  Purchase #3 $149.54   10.119%   $164.672   $164.67   $164.65   $164.70  
  Purchase #4 $129.29   11.180%   $143.7446   $143.74   $143.75   $143.70  
  Purchase #5 $207.74   5.174%   $218.4885   $218.49   $218.50   $218.50  
  Purchase #6 $242.70   6.592%   $258.6988   $258.70   $258.70   $258.70  
  Purchase #7 $162.95   10.468%   $180.0076   $180.01   $180.00   $180.00  
  7 purchase totals = $979.16       $1,060.5501   $1,060.55   $1,060.55   $1,060.60