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 $53.86   12.383%   $60.5295   $60.53   $60.55   $60.50  
  Purchase #2 $147.35   11.838%   $164.7933   $164.79   $164.80   $164.80  
  Purchase #3 $250.36   4.107%   $260.6423   $260.64   $260.65   $260.60  
  Purchase #4 $226.59   4.481%   $236.7435   $236.74   $236.75   $236.70  
  Purchase #5 $75.51   11.351%   $84.0811   $84.08   $84.10   $84.10  
  Purchase #6 $95.40   8.334%   $103.3506   $103.35   $103.35   $103.40  
  Purchase #7 $116.74   10.675%   $129.202   $129.20   $129.20   $129.20  
  7 purchase totals = $965.81       $1,039.3423   $1,039.33   $1,039.40   $1,039.30