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 $130.86   10.647%   $144.7927   $144.79   $144.80   $144.80  
  Purchase #2 $136.95   13.868%   $155.9422   $155.94   $155.95   $155.90  
  Purchase #3 $157.66   12.590%   $177.5094   $177.51   $177.50   $177.50  
  Purchase #4 $225.38   11.350%   $250.9606   $250.96   $250.95   $251.00  
  Purchase #5 $224.67   7.487%   $241.491   $241.49   $241.50   $241.50  
  Purchase #6 $67.60   3.164%   $69.7389   $69.74   $69.75   $69.70  
  Purchase #7 $32.78   7.522%   $35.2457   $35.25   $35.25   $35.20  
  7 purchase totals = $975.90       $1,075.6805   $1,075.68   $1,075.70   $1,075.60